1The aim is not to become someone with no force in them. It is to get a harness on the force and point it at something worth doing.
Anger usually knows something true: this was unfair, this matters to me, this cannot carry on. Keep that part and drop the delivery. The energy can go into the letter, the boundary, the conversation you have been putting off, instead of into whoever happens to be nearest.
Islamic evidence
I plead my grief and sorrow before God (Quran 12:86). Ya'qub neither swallows what he feels nor spends it on the people around him. He takes it somewhere it can be held.
“He said, ‘I plead my grief and sorrow before God. I have knowledge from God that you do not have”
Qur'an 12:86
Psychological evidence
In a pilot randomised trial, an eight week loving kindness programme for people with chronic low back pain reduced both pain and anger. It is a useful hint that a practice aimed at goodwill can move anger without anyone trying to suppress it. The trial was small and preliminary, in one particular patient group.
Carson JW, Keefe FJ, Lynch TR, Carson KM, Goli V, Fras AM, Thorp SR. (2005). Journal of holistic nursing : official journal of the American Holistic Nurses' Association · doi
Review detail
Why it works. Energy that has somewhere to go stops looking for somewhere to leak.