This is a bit of a meta-answer.
I sometimes see developers gain confidence because of their peer group cheering them on, and it's not necessarily a good thing. I mean, of course being positive is a good thing, but there's so much these days that gets blamed on impostor syndrome, and I've seen people I know tweet about how they're overcoming their impostor syndrome and they're actually good at their job, when I've met them, read their code and wouldn't accept it in a pull request.
It's not common, and it's outweighed by the positive side of things, but it's something I've noticed.
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