Is it bad if I don't feel like an impostor? I started graduate school recently. A professor was talking about impostor syndrome and said that everyone goes through it. They made a joke saying that if you don't feel like an impostor, something is wrong. 

Well, I certainly don't feel like an impostor. I'm doing well in my studies and a professor even said that I'm doing "outstanding".

So, is there something wrong with me that I feel confident in my abilities?
This professor was just trying to reassure the folks who are feeling doubtful or worried.

Bottom line: if you feel worried about something, that's okay, it's a common phenomenon, and feeling that way is nothing to worry about; if you don't feel worried about something, great!  No need to feel worried!