Our past could mar our perspective about life and humans, and most times changes our response to how we treat each other. A person who was once betrayed by a friend he trusted, will find it difficult to trust people because of the experience he has had. Most often, bitterness is tied to our negative past experiences, it keeps haunting us to have recurrence of the events each time we try to be who we have always been. Behind every hostile man is a gentle heart that had once been shattered, they become hostile as a means of guiding their heart from being broken over again. We are structured to believe hostility could protect us from being vulnerable, this can be seen in a dog and other animals. Each time they become hostile, they are faced with something they are scared could endanger them, so are humans.
A child was noticed to be bitter over his peers groups each time they go out to play. The teachers got tired of his behavior and each time disciplined him but that never helped. A few months later, a new teacher was employed into the school and was assigned to the class where the hostile boy was, he noticed his bitterness with other children but decided to respond differently. He tried to find out why he was always bitter, and later realized the child lost his mum while he was very young and those who raised him were hostile to him. All he ever knew was hostility, any kind of goodness was strange because he had never been loved.
Occurrence of certain events in our life is what breeds bitterness. A king on hearing the news that his kingdom was about to be seized rented his clothes in bitterness, a man whose temple was defiled became hostile to people, etc. Bitterness is always a way of responding to certain events that are unpleasant.