Habit

Dostoevsky sees a dog in prison that all the prisoners are kicking.
He notices that the dog does not run away from the prisoners, on the contrary, when they approach it, it bends down and assumes the position of being kicked!
One day Dostoevsky approaches it and strokes its head.
The dog looks at him with surprise and fear, moves away from him and whines bitterly.
From that day on, the dog runs away every time it sees Dostoevsky!
The dog was accustomed to mistreatment and was afraid of any other form of attention; when someone treats it nicely, it sees its safety as a threat!

The same is true for humans.  People who have seen mistreatment and distrust their whole lives don't know how to react when they see love. They don't know the world of kindness and trust. They feel strange in it and fear, disbelief, and anxiety take over them. 
In fact, for people, "The good they don't know is more dangerous than the bad they know!"
It's not without reason that sometimes those you mistreat praise you and those you treat well get upset with you because they haven't gotten used to kindness and affection and are strangers to them