"beauty is in the eye of the beholder"which basically means that beauty is something individual to each person, which is true. Some people like blondes, some like brunettes. Some like blue eyes, some like brown eyes. These factors determine how attractive someone is to them.
So what happens if you have green eyes, but only like brown eyes? What if you have brown hair, but only like blondes? You're not going to view yourself as attractive if you only view those with these characteristics attractive. I believe your personal view on what attractive is, reflects on ourselves and if it doesn't meet the standards we expect of an attractive person, we deem ourselves as unattractive. Those who love themselves are either tricking themselves into believing they're good looking or feel their looks meets their standards of attractiveness.