Judging on single traits

There are exceptions to this, but very rarely do others judge you based on single traits.

You don’t hear a lot of people say “That girl has a weird haircut, so I don’t like her as a person.” or “That guy has a weird laugh, so I don’t want to hang out with him”.

People look at you as an entire package. Personality, appearance, social circle, the whole shebang. This might be obvious, but why is to so common to judge ourselves based on single traits?

Note: Keep in mind that I’m not talking about people who judge others on traits like race or gender, that‘s a separate issue. I’m simply talking about how others see you on a daily basis.