Proverbs 14:8

8 The wisdom of the prudent is to observe his way, And the folly of fools is deceit. The nearest idea is that of self-deceit, according to which the lxx, Syr., and Jerome render the word error ("Irrsal"). But מרמה is nowhere else used of self-deception, and moreover is not the suitable word for such an idea, since the conception of the dolus malus is constantly associated with it. Thus the contrast will be this: the wisdom of the prudent shows itself in this, that he considers his conduct (הבין as Pro 7:7, cf. Psa 5:2), i.e., regulates it carefully, examining and considering (Pro 13:16) it according to right and duty; and that on the contrary the folly of fools shows itself in this, that they aim at the malevolent deception of their neighbour, and try all kinds of secret ways for the gaining of this end. The former is wisdom, because from the good only good comes; the latter is folly or madness, because deception, however long it may sneak in darkness, yet at last comes to light, and recoils in its destructive effects upon him from whom it proceeds.

See here, 1. The good conduct of a wise and good man; he manages himself well. it is not the wisdom of the learned, which consists only in speculation, that is here recommended, but the wisdom of the prudent, which is practical, and is of use to direct our counsels and actions. Christian prudence consists in a right understanding of our way; for we are travellers, whose concern it is, not to spy wonders, but to get forward towards their journey's end. It is to understand our own way, not to be critics and busybodies in other men's matters, but to look well to ourselves and ponder the path of our feet, to understand the directions of our way, that we may observe them, the dangers of our way, that we may avoid them, the difficulties of our way, that we may break through them, and the advantages of our way, that we may improve them - to understand the rules we are to walk by and the ends we are to walk towards, and walk accordingly. 2. The bad conduct of a bad man; he puts a cheat upon himself. He does not rightly understand his way; he thinks he does, and so misses his way, and goes on in his mistake: The folly of fools is deceit; it cheats them into their own ruin. The folly of him that built on the sand was deceit.