This is how I see the difference:
You're good at stuff, are confident in what you do, but you don't let that change the way you treat others - that is, you have an ego that can fit through a reasonably sized door.
You're good at stuff, but believe erroneously, based on internal analysis of the available evidence (and tainted by your own perception), that you're terrible at it compared to your peers, and nothing will convince you otherwise.
This craters your confidence and self-esteem, and will also make it so that you tend to buckle in the face of conflict or resistance. It saps your courage, and reduces your grit.
Simon Cooke is an occasional video game developer, ex-freelance journalist, screenwriter, film-maker, musician, and software engineer in Seattle, WA.
The views posted on this blog are his and his alone, and have no relation to anything he's working on, his employer, or anything else and are not an official statement of any kind by them (and barely even one by him most of the time).