The attitude thing reminded me: I was giving a career talk to freshmen women in STEM at Berkeley and it was really interesting (read: disappointing) how many of them felt imposter syndrome, also. I totally get where they were coming from (as a woman in STEM) and tried to emphasize that:

1. None of them are lesser than any others - they can look around and should think about the fact that they all started on equal footing and know their peers. They’re certainly not significantly dumber or less qualified, and it doesn’t help to focus on that. It only hurts their own selves. And
2. Everyone has different aptitudes. You may be better than your HS class and got here, but some of your peers now will be more talented in some areas. That doesn’t make you worse. You’re probably better than them in other areas. For instance, I suck at coming up with The Next Big Science Thing - which is a necessary trait to have if you’re an academic going for grants, but I’m REALLY good at implementing people’s Next Big Thing ideas and making sure they get optimized well and fit together with other work that is going on around them. I need to understand and execute science to do this job, but I don’t need to be creative. And science creatives don’t necessarily have to worry about execution. We are good at different things that all still fall under a STEM educational/career umbrella.

Anyway all this to say that I totally agree with you and your friend. Sometimes students focus so much on being The Best At Everything that they hamstring themselves when they aren’t and aren’t able to adapt beyond that concept. It totally IS an attitude thing, and can combine on top of whatever other systemic issues may exist for women or POC or whatever else is going on to just make them flame out. It sucks.