Also OTP/erlang and elixir and whatsapp use case are very much a match made in heaven -- they were able to get a whole mess of productivity for "cheap" because the core platform they built on came with a robust foundation to build on.

From the follow-up: https://news.ycombinator.com/item?id=33729397

"No one is arguing that WhatsApp’s 50-employee headcount in 2014 means Twitter only needs 50 employees today. That’s a straw man argument. I’m talking mostly about software engineers and designers. Twitter has thousands of them. Everyone I know who has (or still does) work there has told me the same thing: the company is lousy with do-nothing employees and layers of bureaucracy to support their preposterously high headcount and needless managerial fiefdoms." etc.