In training therapist and future social service providers I have come across the bias that the more attractive a client, whether it is physically or in accommodating or feeding into the receivers emotional needs, whatever makes a person feel good will determine their gravitational pull towards that individual. It is subjective, however the outer appearance is usually the first standard. Secondly as a matter of fear or areas that create anxiety in us, we steer away from those that are not attractive to us or scare us. For example, people who are overweight, handicapped, of an unknown ethnic background, etc