I think about this a lot. I've been making my living in #bioinformatics for almost twenty years (!) with a #PhD for ten: if I'm not "good at it" by now, I'm doing something seriously wrong. But #impostor #syndrome never stops whispering in the back of my head. Probably that's true of most competent people in most fields.
The problem is that while self-doubt may be necessary for competence, it's not sufficient. So you never really know.
https://www.quora.com/Does-having-a-Ph-D-in-a-subject-make-you-good-at-it/answer/Daniel-Dvorkin-3
@medigoth Maybe "capable" is a better way to frame it - capable of doing and capable of self-learning, in a given field. Being "good at" is so subjective and depends so much on the point of view...
