Facebook has the value of “Move Fast.” Getting a project going at Facebook can be extremely fast, but the full process of rolling out a product can actually take quite a bit of time. If WhatsApp had a similar motto, it would be “Move Slow and Deliberate.” We take a lot more time up front in the design phase, mainly because we’re more adverse to pivoting in the development phase. When we hand off the design to engineers, we really try to deliver as much of a finished spec and mocks as possible. The advantage of this is it causes less churn in engineering, which engineers appreciate. The potential downside is that engineers can feel less involved in the process of designing the product and might feel more isolated from the product decisions.
This causes behaviors in the user interface that might not make sense for people who don’t understand the underlying technology. For example, when you log into WhatsApp on a new device, you don’t immediately have all of your old messages. That’s because they’re still on your old device — there isn’t a copy on the server.
Some of the product problems I’ve encountered at WhatsApp have been like nothing I’ve ever dealt with before. For example, end-to-end encryption has many challenging side effects. Messages are stored on the user’s own device and WhatsApp doesn’t store users’ messages once they’ve been delivered.