- Going with the gut instead of listening to others. I had the surrealistic experience of a bunch of extremely senior folks around a company telling me not to join a team I had done a project for. I should have listened, esp. in light of the fact that the folks advising were not only not from the same team, but in many cases actively disliked each other (i.e. this was not a conspiracy).

- Ignoring the office politics. I thought, naively, that doing above and beyond technically and being frank about situations around me would get me somewhere. It turned out that someone I had put in a not-so-favorable crosshair, while describing my fairly significant cross-team collab efforts, was chummy with my manager's manager, and it blew up in my face... see next item...

- I had the misfortune of deciding to report to an average-engineer-turned-mediocre-manager. Typical deer-in-headlights-look turnstile manager - i.e. the kind that takes plenty of credit, but doesn't shield you from anything. The guy was laughably terrible, because it was extremely obvious when he was trying to screw you in 1:1s. I was young and stupid and it ended pretty nasty: vindicative passive-agressive bullshit, blame game and damaging rumors that impacted my professional relationship with the rest of my ex-teammates.

- Not setting priorities straight. I had a personal situation that involved a lot of travel. It didn't even matter that I was exceeding expectations - visibly, I was never there, and that is all that ultimately mattered.

But these are all symptoms! The biggest mistake was not identifying a mentor. Not a technical mentor, but someone seasoned, high enough in the social ranking, and vibrant enough (i.e. not semi-retired and clinging to the job) to advise, help and teach how to navigate a large megacorp with its feudal cliques, ol' boy's club politics and Machiavellian egoes.