According to Wikipedia: "The halo effect is a cognitive bias that involves one trait influencing others in one's judgement of another person or object. First noted by Edward Thorndike in the 1920s, the halo effect has since been applied to a variety of other fields".

This is a primary reason why you should really, really care how you look. I am not saying that it involves wearing a suit 24/7, but even if you are a hacker-type, in real life, those things matter.