You could potentially miss out on some great employees if you let your ego get in the way of making an objective hiring decision. I've been working with T-SQL for over 10 years and I've helped to make a lot of money for the companies I've worked for. I've also had a very wide variety of experience which I think makes me a valuable asset, but it also means that I don't have to write that particular piece of code frequently enough to have it memorized. I don't mind admitting that I don't know everything. I figure out what I don't know.