Jean Lee was the 19th engineer to join WhatsApp when it had 20 million users. By the time she left, it had 1.2 billion.
Most engineers dream of joining a unicorn startup before it explodes. Jean Lee lived it—watching WhatsApp grow from a promising messaging app to a $19 billion acquisition by Facebook, all while helping build the engineering culture that made it possible.
In this interview, Jean shares what really separates the top 1% of engineers from the rest, why following coding trends is a recipe for failure, and how simplicity—not complexity—became WhatsApp's secret weapon for serving over a billion users.
Watch the full interview now on EO's YouTube channel! Below is the complete transcription of the interview. Minor edits have been made for clarity and readability.
Key Highlights:
"I was the 19th engineer to join WhatsApp. We may have had around 20 million users at the time, and by the time I was leaving the company, we had 1.2 billion active monthly users."
"Influence is about likability and credibility. When I ask Peter, I know Peter will deliver. I know he's dependable and he's not gonna make me feel like shit."
"It drives me crazy when I see these videos, like top 5 trends or top 5 languages to follow, because I don't think that's what really will help you be successful."
"Blindly following trends is recipe for failure because you're always going to be a step behind."
"If I were to sum up the WhatsApp engineering culture in one word, it's challenging, but I would say it was simplicity."
"When WhatsApp got acquired for $19 billion I actually wasn't even sure what a billion dollars was."
"Influence is about likability and credibility. When I ask Peter, I know Peter will deliver. I know he's dependable and he's not gonna make me feel like shit."
"It drives me crazy when I see these videos, like top 5 trends or top 5 languages to follow, because I don't think that's what really will help you be successful."
"Blindly following trends is recipe for failure because you're always going to be a step behind."
"If I were to sum up the WhatsApp engineering culture in one word, it's challenging, but I would say it was simplicity."
"When WhatsApp got acquired for $19 billion I actually wasn't even sure what a billion dollars was."
The Real Secret to Engineering Influence
After working with thousands of engineers over 17 years, what separates those who get promoted and land dream opportunities from those who don't?
Jean Lee: I've been working in tech for 17 years, so over the years I've probably worked with thousands of engineers. Every single person wants some kind of influence. It could be influence in terms of I want to get a promotion, that's a form of influence you want to influence your management. Or I want to get a different job.
So that's part of our curriculum, influence, and we say influence is about likability and credibility. When I ask Peter, I know Peter will deliver X. I know he's dependable and he's not gonna make me feel like shit. He's not going to be an asshole and he's going to be pleasant to work with.
So likability plus credibility can bring you a lot of influence. People will come to you for new opportunities. If I'm building a new startup, I'm thinking about who do I want on my team, they're gonna think of people who have the likability and the credibility together. Because if you only have one or the other, you're OK. You might be able to tag along, but you're not gonna be the first person they think of.
So that's part of our curriculum, influence, and we say influence is about likability and credibility. When I ask Peter, I know Peter will deliver X. I know he's dependable and he's not gonna make me feel like shit. He's not going to be an asshole and he's going to be pleasant to work with.
So likability plus credibility can bring you a lot of influence. People will come to you for new opportunities. If I'm building a new startup, I'm thinking about who do I want on my team, they're gonna think of people who have the likability and the credibility together. Because if you only have one or the other, you're OK. You might be able to tag along, but you're not gonna be the first person they think of.
Why Chasing Coding Trends Will Destroy Your Career
You've spoken against following the typical 'top 5 programming languages' advice. What should engineers focus on instead?
Jean Lee: So I do recommend, even if you are really good at all of them, please choose one. What is your thing? What do you want to be known for?
As I started getting more involved with YouTube, I've been watching more content that drives me crazy when I see these videos, like top 5 trends or top 5 languages to follow, because I don't think that's what really will help you be successful.
It's not about which language you know because as a hiring manager, I'm often trying to just understand, are you a smart engineer? Can you code? Because what languages we're using today may not be applicable tomorrow. So I want to be able to work with people who can learn new things, pick up new skills, and that's what I'm interviewing for when I talk to new software engineers.
Similar principles apply to success. Blindly following trends is recipe for failure because you're always going to be a step behind. So I encourage people to be inquisitive and explore your passions. What are you good at? What do you enjoy doing and follow that.
As I started getting more involved with YouTube, I've been watching more content that drives me crazy when I see these videos, like top 5 trends or top 5 languages to follow, because I don't think that's what really will help you be successful.
It's not about which language you know because as a hiring manager, I'm often trying to just understand, are you a smart engineer? Can you code? Because what languages we're using today may not be applicable tomorrow. So I want to be able to work with people who can learn new things, pick up new skills, and that's what I'm interviewing for when I talk to new software engineers.
Similar principles apply to success. Blindly following trends is recipe for failure because you're always going to be a step behind. So I encourage people to be inquisitive and explore your passions. What are you good at? What do you enjoy doing and follow that.
The 'No Gimmicks' Philosophy That Built WhatsApp
WhatsApp famously avoided feature bloat while competitors added everything. How did this focus shape the product?
Jean Lee: At WhatsApp, we actually had a note written by one of the founders. We wrote 'no gimmicks,' and we had it posted on the wall. We decided we're not gonna do games, we're not gonna do gimmicks. We're not gonna throw in a bunch of features just to appease every single person.
The way we are going to appease every single person is by focusing on the core utility features, like does the messaging actually work? Can you call someone and can you actually hear them? I guess another word you can say is we focused on quality we wanted to drill in to make sure it worked every single time rather than adding on a bunch of new features.
We would get a lot of emails from people all over the world and they would tell us there was a natural disaster, nothing was working, the phone lines were down, but I was able to use WhatsApp to call the firefighters and I was rescued or I was in a car accident and I was rescued, so I do believe it worked.
The way we are going to appease every single person is by focusing on the core utility features, like does the messaging actually work? Can you call someone and can you actually hear them? I guess another word you can say is we focused on quality we wanted to drill in to make sure it worked every single time rather than adding on a bunch of new features.
We would get a lot of emails from people all over the world and they would tell us there was a natural disaster, nothing was working, the phone lines were down, but I was able to use WhatsApp to call the firefighters and I was rescued or I was in a car accident and I was rescued, so I do believe it worked.
From 3-Person Startup to IBM to WhatsApp: The Goldilocks Problem
You went from a tiny startup to IBM, then to WhatsApp. What were you looking for in each transition?
Jean Lee: So when I was in college, I actually interned for a three-person startup and we had a lot of fun. I loved the ownership, the autonomy. I could really see the impact of my work. I also felt like we were lacking direction and leadership and mentorship. And that's part of the reason why I joined IBM.
And when I did join IBM, I felt like there was great mentorship, but I lacked the autonomy. So WhatsApp for me struck a balance because at the time, I was the 19th engineer. It was small enough where I could see the impact of the work, but the fact Founders had a lot of experience. They were both from Yahoo. They had a lot of experience working in tech, and I felt like that would be a great balance for me to find both ownership and mentorship.
And it's not like we had one on one every week. It wasn't a formal mentorship, but just by being there in a small company and observing and watching, similar to my upbringing, just learning how they operate, how they lead, was a really great opportunity for me and I learned so much by just being there.
And when I did join IBM, I felt like there was great mentorship, but I lacked the autonomy. So WhatsApp for me struck a balance because at the time, I was the 19th engineer. It was small enough where I could see the impact of the work, but the fact Founders had a lot of experience. They were both from Yahoo. They had a lot of experience working in tech, and I felt like that would be a great balance for me to find both ownership and mentorship.
And it's not like we had one on one every week. It wasn't a formal mentorship, but just by being there in a small company and observing and watching, similar to my upbringing, just learning how they operate, how they lead, was a really great opportunity for me and I learned so much by just being there.
Scaling Culture: From 20 Million to 1.2 Billion Users
How did WhatsApp maintain its engineering culture during explosive growth, especially when you were building the London office?
Jean Lee: We may have had around 20 million users at the time and by the time I was leaving the company, we had 1.2 billion active monthly users. There were several values I think that was key to the success of WhatsApp and as we experienced the growth, I think it was really important to be able to hold on to our engineering culture and that was part of my big focus as well when I was starting the new office in London.
There in 2018 we grew the office to about 100 engineers in a couple of years and in that short period of time we were hiring new engineers every week and one thing that we tried to really do was to make sure that everyone understands the engineering culture for WhatsApp.
I think it was pretty special and if I were to sum up the WhatsApp engineering culture in one word, it's challenging, but I would say it was simplicity.
There in 2018 we grew the office to about 100 engineers in a couple of years and in that short period of time we were hiring new engineers every week and one thing that we tried to really do was to make sure that everyone understands the engineering culture for WhatsApp.
I think it was pretty special and if I were to sum up the WhatsApp engineering culture in one word, it's challenging, but I would say it was simplicity.
How did you achieve that simplicity in practice across such a large engineering organization?
Jean Lee: So simplicity can mean a lot of different things, but one way of achieving simplicity is really prioritizing. It's easy for us to say I'm going to do 10 different things and be really great at it, but it's actually much harder to be focused on few core features and few core offerings that we will offer and prioritize them ruthlessly.
We had a clear decision maker who gave us clear messaging about which features we're going to deliver, and we came up with these features intentionally as well. We had ideas like, OK, we want to make sure even someone in the middle of nowhere with bad internet connection on an old device should be able to use our app. So we wanted to prioritize the user experience, so even people in remote places with body internet connection on older devices can use our app.
Also, we like to talk about can a grandma in the middle of nowhere use this feature and that was our Guiding principle for how we prioritize our work.
We had a clear decision maker who gave us clear messaging about which features we're going to deliver, and we came up with these features intentionally as well. We had ideas like, OK, we want to make sure even someone in the middle of nowhere with bad internet connection on an old device should be able to use our app. So we wanted to prioritize the user experience, so even people in remote places with body internet connection on older devices can use our app.
Also, we like to talk about can a grandma in the middle of nowhere use this feature and that was our Guiding principle for how we prioritize our work.
How did this clarity help individual engineers make better decisions?
Jean Lee: We made sure that every single person understood what we're building and where we're going. And I also implemented that in my personal team as engineering manager as well. I let people know these are the things that we're building, and this is our long-term overall goal.
So when they are working, I can't always be there to hold their hand and guide them, but when they're working, they can prioritize their own work when they have competing projects. Or features or priorities, they can say, these are our guiding values or priorities, and I know exactly which one I need to prioritize.
And it would work also when you're working cross-functionally. If someone's asking you for help or giving you new ideas or suggestions, you understand what needs to be done for not just yourself but for your team and a company as a whole. So achieving simplicity through prioritizing was one of the key factors for success for us.
So when they are working, I can't always be there to hold their hand and guide them, but when they're working, they can prioritize their own work when they have competing projects. Or features or priorities, they can say, these are our guiding values or priorities, and I know exactly which one I need to prioritize.
And it would work also when you're working cross-functionally. If someone's asking you for help or giving you new ideas or suggestions, you understand what needs to be done for not just yourself but for your team and a company as a whole. So achieving simplicity through prioritizing was one of the key factors for success for us.
The $19 Billion Moment: When Success Becomes Confusing
What was it like when you heard about the Facebook acquisition? How do you even process that kind of news?
Jean Lee: When WhatsApp got acquired for $19 billion I actually wasn't even sure what a billion dollars was. The type of amount of money that you can't really tangibly describe, how much is a billion dollars.
The moment that I heard the acquisition news, I was sitting in the conference room. It was really weird. The founders looked a little weird. I couldn't articulate at the time because I didn't know what was happening, but they're like waving their arms and like saying you need to get into this conference room.
I couldn't believe my ears. I wasn't sure what was happening, but when I heard the news, OK, Facebook's buying us for $19 billion. And I was sitting in the conference room thinking, how much is that? And what does that mean for me?
Like, I was pretty young at the time, so I didn't know how much shares I actually exactly had. And I wasn't really sure what that meant for me, and I was trying to calculate the number. What does that mean for me? And I couldn't do the math. So, yeah, it was an incredible opportunity and it was really exciting to be there. And it does really change your life.
The moment that I heard the acquisition news, I was sitting in the conference room. It was really weird. The founders looked a little weird. I couldn't articulate at the time because I didn't know what was happening, but they're like waving their arms and like saying you need to get into this conference room.
I couldn't believe my ears. I wasn't sure what was happening, but when I heard the news, OK, Facebook's buying us for $19 billion. And I was sitting in the conference room thinking, how much is that? And what does that mean for me?
Like, I was pretty young at the time, so I didn't know how much shares I actually exactly had. And I wasn't really sure what that meant for me, and I was trying to calculate the number. What does that mean for me? And I couldn't do the math. So, yeah, it was an incredible opportunity and it was really exciting to be there. And it does really change your life.
How did sudden financial freedom change your relationship with work?
Jean Lee: Life there are many things money can change or doesn't change as well. It can bring you a certain fulfillment and stability, but there is a lot more that we need beyond that. What do you wanna do if you don't work? Yeah, you can stay home, watch TV, but after a while, TV is kind of boring, so I think it's about how you view your work.
I don't feel like I'm working. I'm just having fun. That's why you need to find something that's interesting for you, right? Why does Bill Gates work? He's still doing so much. He's working all the time, but I don't know Bill Gates and I don't know why he's working, but I would suspect most of these people who continue to work, they don't see it as work. They see it as a meaningful part of their life.
I think it was a turning point for my life because I was never financially free growing up, so having the financial freedom was a little bit confusing at times. I did have to go experiment a lot and explore again to redefine the meaning of work for myself, to understand how do I want to spend my time.
I don't feel like I'm working. I'm just having fun. That's why you need to find something that's interesting for you, right? Why does Bill Gates work? He's still doing so much. He's working all the time, but I don't know Bill Gates and I don't know why he's working, but I would suspect most of these people who continue to work, they don't see it as work. They see it as a meaningful part of their life.
I think it was a turning point for my life because I was never financially free growing up, so having the financial freedom was a little bit confusing at times. I did have to go experiment a lot and explore again to redefine the meaning of work for myself, to understand how do I want to spend my time.
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