There's a not so fine line between being nice and being naive when making decisions about your friends, partners and social circles.
Some folks deceive themselves into thinking that they are being nice when they carry on with relationships that are unfruitful and unproductive. But when you refuse to walk away from someone that you know lacks integrity, is cruel or manipulative it is because you fear the possibility of being alone.
Sadly when you chose to be influenced by people who don't treat you well, their bad behavior rubs off and you begin to adopt their habits and ways of treating others. In addition, you likely sabotage potential quality friendships by putting pressure on others to compensate for the lack of genuineness, support and care.
Birds of a feather flock together... And yet when eagles choose to spend their time and resources knowingly on ducks, they begin to look, act and quack like ducks.