Funnily enough, when I do design interviews, I often ask them to design a chat client - not the whole design, but bits and pieces, like the db schema or the API

Funnily enough, when I do design interviews, I often ask them to design a chat client - not the whole design, but bits and pieces, like the db schema or the API of the service. What the interviews invariably show is that a chat client is not simple. It's extremely complicated, especially when you want it to work at scale. If you think it's a "simple" app, go ahead, try to make one - even on a whiteboard. I can completely understand why instant messaging can get you $700 million in revenue. As for the losses -- they are invested in the future of the company and I think are justified. "How hard can it be?" is something we ask about "simple" stuff everyday, and the answer if you dig deeper is almost always "Much harder than you think."