John Gill Commentary Proverbs 29:11

"A fool uttereth all his anger; But a wise man keepeth it back and stilleth it." — Proverbs 29:11 (ASV)

A fool utters all his mind
At once; tells all he knows, all that is in his breast; whatever he thinks, and all that he intends to do; what or whom he loves or hates. Or, "a fool brings out all his wrath"; so the Targum, Septuagint, Syriac, and Arabic versions: he cannot restrain it, nor hide it; it breaks out at once, even all of it, and is soon known, as in (Proverbs 12:16) ; but a wise [man] keeps it in until afterwards ;
reserves his mind, and thoughts, and designs, to himself; and does not discover them until a proper opportunity offers, when to disclose them is most to advantage; or he restrains his wrath and anger, defers showing it to a proper time, when it may answer a better purpose, and he may do it without sin.