Ask HN: How do you stop selling yourself short amidst negative criticism?

I've heard this multiple times. Don't sell yourself short, if you're looking to find a better job, promotion, whatever you're looking to get from others in life.

I've gotten plenty feedback about my job experience, saying it indicates very slow progress and complacency (and that's just the general idea). Despite all of this I'm also being told not to sell myself short. If your feedback gives you a harsh reality check how can you resist not to? How do you "sell up" when people give you few positive things to say about yourself?