Judging people based on your internal biases can lead you to form misinformed and wrong opinions of them. This could cause you to lose a potential friend, employee, client, etc.
Think about and identify your own biases.
It may not be easy to identify your biases, as a lot of them are unconscious ones. However, the next time you find yourself in a position where you have to make a judgment about someone, do your best to only judge them on their skills and abilities, instead of something arbitrary like looks or gender.