A friend has asked me after reading the most recent post to explain where this bitterness comes from. I have decided to answer the question here so others may be able to make an input. Well bitterness may come from others as I mentioned somewhere. And bitterness breed with hatred directed towards someone, or something that might have hurt us...or that may be hurting us. What is common is that most people who are bitter hardly identify where their bitterness comes from. And this makes it a disease hard to cure, a scar difficult to live with.
The primary human instinct is to give back evil for evil. Eye for eye. Tooth for tooth. When we feel slighted, the wound gets deep and spurs us towards the sense of revenge. Thus we become bitter, resentful and willing to wield negative energy.
Bitterness may also result from a certain frustration that issue from our condition of being human. We are limited in every sense and could not get or afford all that we want... What happens often is that we feel low, frustrated and may even turn mean on others, blaming everyone for being the cause of our failure... but the truth is, we might not have accepted our condition of being human fully and freely.
Bitterness comes from within as from without. From within due to our ill-begotten fate which is blessedness also: our humanity. We might be bitter with an unacceptable illness, we might be bitter due to our pride which does not permit us to let others in... etc. But there is the bitterness which is a reaction to the way that society and others treat us.