Yeah, the second one is really the most bitter pill - work for a year or more, see that the PMF or the actual product isn't going to meet the needs; raise red flags, nobody cares (or worse, people actively fight you and torpedo you) and then you get to see it literally do nothing in production.

I have seen this a lot in the mid sized business (<300 employees usually) and its the "we have enough money and no accountability and terrible processes to even understand the world" but my favorite one is my friend spent six months building a product offshoot from a core product, got pulled into meetings with directors to tell him to shut up about how it wasn't going to work for the target market, and when he finished they sold 4 units.

4 units.