It's funny how grad school is designed to bring out the impostor in you, kind of like a negative image of the different kinds of "impostor" listed. Obviously each of these is false in their own way, but these are messages that you will be given / experience during your PhD, so it's no wonder how people come out the other end thinking like this:

1. "The Expert": your advisor/other professors/students will make fun of you or berate you if you don't know "everything" i.e. if asked to list relevant sources you list twelve and forget the thirteenth.

2. "The Perfectionist": your advisor will never say that a work is "good" and there are always ways to improve everything, the good parts will go unmentioned while the warts will be called out for repair until eventually you run out of time and ship it.

3. "The Superperson": everyone else is always working, so why aren't you?

4. "The Natural Genius": these are the words that your advisor and other professors will use to describe "successful" students: genius, insightful, gifted. Words your advisor will never use to describe someone positively: hard-working. Hard-working is assumed. Everyone is hard-working. Everyone puts in a lot of effort. Get over it.

5. "The Rugged Individualist": Only work that you and you alone did "counts" for your PhD, and credit is zero-sum. Debate carefully the authors you add to your paper because they will take some of the "success" from your work.