I would also say that interviewing is hard because we have limited time to decide upon each person and what we judge is (apart from some technical qualities) not what kind of person really is but rather what we believe the person is (based on our limited human perception). And with handful of techniques a person can be really cool from at the first sight (trendy, rock star, etc.) but might be a bad choice in the long run.
Limited time makes it immensely difficult. However, I've found my prejudices against people not like myself have gone way past the interview. I had one intern for 2-3 months before I realized I was really lucky to have him, and it was only because someone else pointed it out.
This person didn't have the right education (classes, not pedigree) nor did he project a passion for coding on his sleeve, but it turned out he was disciplined, a fast autodidact and had a very good sense of priorities. I couldn't have been more wrong about his potential.
It's not just that. I think we too often discount people's ability to grow. My suspicion is we probably place too much emphasis on keeping the wrong people out and not enough on developing the people we have.
