FWIW there are some similarities with getting a bad review in a large bureaucratic company (I know for HN readers this either doesn't apply, or they wish it didn't!), one common thread that I would emphasize is that even if the headline reason for the firing or crappy review (FOCR) is complete BS or political or whatever, there is very likely something that you did have control over that either precipitated the FOCR or created an excuse for it, but the immediate shame/rage/pain of the whole FOCR may make that hard to see. Expect to need to sit on the experience for several years before the full value to you can be gleaned. Having been through this in a couple of guises I have definitely learned some real lessons about both myself and the behaviour of teams, managers, and companies.

I suspect the same can be true for some startup failures... maybe in my next adventure I will find out.