As another commentator said, the problem is often less the person and more the fact that saying 'I don't know' is a massive negative in most interview settings.

As another commentator said, the problem is often less the person and more the fact that saying 'I don't know' is a massive negative in most interview settings. It was something I noticed when I was interviewing for job positions. Any time I said 'I'm not sure' or 'I don't know' and followed up with 'I'd have to look at the manpage' or 'look up the documentation' either the interviewer would express disappointment or continue to press the question in order to get even a wrong answer. Many interviewers are looking for you to perfectly regurgitate canned answers rather than admit when you don't have something memorized.