"Be not quick to anger, for anger lodges in the bosom of fools!" -Ecclesiastes 7:9
"If a clever man is angry, his wisdom quits him." -Talmud, Nedarim 22b
"Calm, persevering patience is generally a virtue, but especially so for Torah study, for anger causes errors in judgment and leads one to forget one's learning." -The Pirkei Avos Treasury, p.416
Anger is also an exceptionally bad quality. It is fitting and proper that one move away from it and adopt the opposite extreme. He should school himself not to become angry even when it is fitting to be angry. If he should wish to arouse fear in his children and household - or within the community, if he is a communal leader - and wishes to be angry at them to motivate them to return to the proper path, he should present an angry front to them to punish them, but he should be inwardly calm. He should be like one who acts out the part of an angry man in his wrath, but is not himself angry. The early Sages said: Anyone who becomes angry is like one who worships idols. They also said: Whenever one becomes angry, if he is a wise man, his wisdom leaves him; if he is a prophet, his prophecy leaves him. The life of the irate is not true life. Therefore, they have directed that one distance himself from anger and accustom himself not to feel any reaction, even to things which provoke anger. This is the good path. -Rambam Hilchot Deot
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