Just how sexy is confidence? Just about everyone from feminists to pickup artists agrees that it is of utmost importance. Roissy writes that you should be more confident even if you have no objective reason for it:

Be irrationally self-confident

No matter what your station in life, stride through the world without apology or excuse. It does not matter if objectively you are not the best man a woman can get; what matters is that you think and act like you are. Women have a dog’s instinct for uncovering weakness in men; don’t make it easy for them. Self-confidence, warranted or not, triggers submissive emotional responses in women.

All right, let's test that hypothesis. What if a guy who is not all that bad looking but has a very uninteresting personality convinced himself to the inmost depths of his soul that he is extremely sexy and irresistible to women? Would they actually desire him, or at least be less repelled? Here is a good test case, and the answer is "hell fucking no", but if you are still not convinced there is further data available.