Mind - The Hebrew word is used sometimes for "mind" or "reason," sometimes for "passion," or "wrath." The reticence commended would include both; but the verb "keepeth it in" (rendered "stilleth," in Psalm 65:7) is slightly in favor of the second of the two senses.

A fool uttereth all his mind - A man should be careful to keep his own secret, and never tell his whole mind upon any subject, while there are other opinions yet to be delivered; else, if he speak again, he must go over his old ground; and as he brings out nothing new, he injures his former argument.

A fool uttereth 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 keepeth it in till 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.

He is a fool who tells every thing he knows, and can keep no counsel.

(Compare Proverbs 12:16; Proverbs 16:32).
mind--or, "spirit," for anger or any ill passion which the righteous restrain.

11 All his wrath the fool poureth out;
But the wise man husheth it up in the background.
That רוּחו is not meant here of his spirit (Luther) in the sense of quaecunque in mente habet (thus e.g., Fleischer) the contrast shows, for ישׁבּחנּה does not signify cohibet, for which יחשׁכנּה (lxx ταμιεύεται) would be the proper word: רוּח thus is not here used of passionate emotion, such as at Proverbs 16:31; Isaiah 25:4; Isaiah 33:11. שׁבּח is not here equivalent to Arab. sabbah, αἰνεῖν (Imman., Venet., and Heidenheim), which does not supply an admissible sense, but is equivalent to Arab. sabbakh, to quiet (Ahron b. Josef: קטפיאון = καταπαύειν), the former going back to the root-idea of extending (amplificare), the latter to that of going to a distance, putting away: sabbakh, procul recessit, distitit, hence שׁבּח, Psalm 89:10, and here properly to drive off into the background, synon. השׁיב (Fleischer). But בּאחור (only here with ב) is ambiguous. One might with Rashi explain: but the wise man finally, or afterwards (Symmachus, ἐπ ̓ ἐσχάτων; Venet. κατόπιν = κατόπισθε), appeaseth the anger which the fool lets loose; i.e., if the latter gives vent to his anger, the former appeases, subdues, mitigates it (cf. בּאחרנה, לאחור, Isaiah 42:23). But it lies still nearer to refer the antithesis to the anger of the wise man himself; he does not give to it unbridled course, but husheth it in the background, viz., in his heart. Thus Syr. and Targ. reading בּרעינא, the former, besides יחשּׁבנּה (reputat eam), so also Aben Ezra: in the heart as the background of the organ of speech. Others explain: in the background, afterward, retrorsum, e.g., Nolde, but to which compescit would be more appropriate than sedat. Hitzig's objection, that in other cases the expression would be בּקרבּו, is answered by this, that with באחור the idea of pressing back (of אחוּר) is connected. The order of the words also is in favour of the meaning in recessu (cordis). Irae dilatio mentis pacatio (according to an old proverb).