truth and lies

I wonder why it's soo easy to believe the negative stuff people say, yet the nice things are taken with skepticism . When a guy calls us ladies beautiful we chalk it up to there tendencies to do anything to get in our pants instead of thinking, maybe i do actually look great today. But when other females refer to us as "dumb" "simple" "slow" or the infamous "b**ch" we are hurt and believe it. why is this so. Why do we lack faith in ourselves???