I just read my last undergrad paper from 10(!) years ago.
I'm glad I didn't know how bad I was at everything, otherwise I would have despaired of pursuing further degrees.

A PhD is a terminal degree because by that point you've wised up to how dumb you actually are.

95% of PhD's are finished as a result of the sunk cost fallacy.

You lose the sense of being an imposter not because you realize you are really super qualified; you just realize everyone else is also an imposter and so you actually fit in.

I'm not bitter or mad or anything like that. I'm extremely grateful for the opportunities I've been granted and would do it all over again (maybe take a few different profs but that's a different story.)

It's just not what I thought it would be like when I started my undergrad.