It's very much a cultural thing to which degree it's expected to come off as super-confident. Americans who apply for jobs over here, for example, tend to overdo it a lot, and come off as ridicolous rather than confident. (same is true, to a lesser degree, for germans)

For me, it was stressful, I disliked it in germany, and doubt I'd like working in USA. I realize people are different, but for me personally, it's a lot more pleasant to work in an environment where it's not merely accepted, but indeed -expected- that you're insecure and uncertain now and then. And being so, doesn't imply that one ain't, infact, entirely awesome.