Bitterness is self induced misery, and it produces chain sinning. A chronically bitter person is his own worst enemy and he becomes difficult to maintain a relationship with. Finally it was used of personal experience when something was unpleasant and undesirable. In our language the concept of mental bitterness comes from the idea of something that has a sharp or unpleasant taste. We speak of something being bitter if it causes us grief or is hard to bear.
Bitterness is just resentment that has been held on to.
It has become rancid and rotten. It is kept in and it gets worse. The links in the chain continue. There is a connection between bitterness and hatred, and a very clear biblical identification between hatred and murder. What I am saying is that hurt can lead to murder.