Simplicity is part of it but it's really also the business model. With good focus they exploited a unique opportunity at just the right moment: SMS arbitrage. T

Simplicity is part of it but it's really also the business model. With good focus they exploited a unique opportunity at just the right moment: SMS arbitrage. To offer "free" messaging when carriers were beginning to offer affordable data plans for third party apps, yet still trying to disproportionately monetize SMS. And this came with a very, very strong network effect. If carriers had proactively disrupted their business model and offered free/cheap SMS sooner, it's unlikely that WhatsApp would have succeeded despite their simplicity and focus. This is why they never took off in the U.S., where carriers did away with SMS fees faster. Having said that, focus is absolutely a reason why WhatsApp beat out its other free-messaging app competition. But the "mind-boggling earn out" is more about the business model -- network effects, exploiting incumbent blindspots, etc.