The non-wisdom which, having brought about disasters by its own perverseness, then turns round and "fretteth," i. e., angrily complains against the Providence of God.
Perverteth - Rather, "overturneth," "maketh to fail."

The foolishness of man - Most men complain of cross providences, because they get into straits and difficulties through the perverseness of their ways; and thus they fret against God; whereas, in every instance, they are the causes of their own calamities. O how inconsistent is man!

The foolishness of man perverteth his way,.... The sinfulness of his heart and nature; the folly which is bound up in it causes him to go astray out of the way in which he should go, or makes things go cross with him; so that the ways he takes do not prosper, nor his schemes succeed; but everything goes against him, and he is brought into straits and difficulties;
and his heart fretteth against the Lord; laying all the blame on him; and ascribing his ill success, not to his own sin and folly, but to divine Providence, which works against him; and therefore frets and murmurs at him; and, instead of charging his own ways with folly, charges the ways of God with inequality; see Ezekiel 18:25.

Men run into troubles by their own folly, and then fret at the appointments of God.

perverteth . . . way--turns him back from right (Proverbs 13:6; James 1:13); and he blames God for his failures.

3 The foolishness of a man overturneth his way,
And his heart is angry against Jahve.
Regarding סלף, vid., at Proverbs 11:3; also the Arab. signification "to go before" proceeds from the root conception pervertere, for first a letting precede, or preceding (e.g., of the paying before the delivery of that which is paid for: salaf, a pre-numbering, and then also: advanced money), consisting in the reversal of the natural order, is meant. The way is here the way of life, the walking: the folly of a man overturns, i.e., destroys, his life's-course; but although he is himself the fabricator of his own ruin, yet the ill-humour (זעף, aestuare, vid., at Psalm 11:6) of his heart turns itself against God, and he blames (lxx essentially correct: αἰτιᾶται) God instead of himself, viz., his own madness, whereby he has turned the grace of God into lasciviousness, cast to the winds the instruction which lay in His providences, and frustrated the will of God desiring his good. A beautiful paraphrase of this parable is found at Sir. 15:11-20; cf. Lamentations 3:39.

Perverteth - Blasts his designs and enterprises. Fretteth - He ascribes his unhappiness not to his own sin, but to God and his providence.