One more warning. The sin is not against man, nor dependent on man's detection only. The secret sin is open before the eyes of Yahweh. In the balance of His righteous judgment are weighed all human acts.
Pondereth - Note the recurrence of the word used of the harlot herself (see Proverbs 1:6 note): she ponders not, God does.

For the ways of a man - Whether they are public or private, God sees all the steps thou takest in life.

For the ways of man [are] before the (m) eyes of the LORD, and he pondereth all his goings.
(m) He declares that unless a man joins to his wife both in heart and in outward conversation, he will not escape the judgments of God.

For the ways of a man are before the eyes of the Lord,.... Both good and bad; the ways of a chaste and virtuous man, who cleaves to his own wife and shuns the harlot, which are approved of by the Lord; and the ways of a lewd man, all the impure thoughts, desires, and contrivances of his mind, and all the steps he takes to commit lewdness, and all the filthy actions he is guilty of, these are all open and naked to the omniscient God: the adulterer seeks the twilight, and flatters himself with secrecy, not considering that the eye of God is upon him; there are many, that, were their filthy actions known to men, they would be ashamed of them; and this consideration greatly deters from them, and puts them upon secret ways of committing them; much more should the consideration of the divine omniscience weigh with them to avoid them; which is the argument here made use of;
and he pondereth all his goings; he not only sees them, but takes notice of them, and observes them, and ponders them in his mind, and lays them up there, in order to bring to an account for them hereafter; yea, he weighs them in the balance of justice, and will proportion the punishment unto them, according to the rules of it; when it must go ill with those that follow such lewd practices, Hebrews 13:4.

The reason, God's eye is on you,

That the intercourse of the sexes out of the married relationship is the commencement of the ruin of a fool is now proved.
21 For the ways of every one are before the eyes of Jahve,
And all his paths He marketh out.
22 His own sins lay hold of him, the evil-doer,
And in the bands of his sins is he held fast.
23 He dies for the want of correction,
And in the fulness of his folly he staggers to ruin.
It is unnecessary to interpret נכח as an adverbial accusative: straight before Jahve's eyes; it may be the nominative of the predicate; the ways of man (for אישׁ is here an individual, whether man or woman) are an object (properly, fixing) of the eyes of Jahve. With this the thought would suitably connect itself: et onmes orbitas ejus ad amussim examinat; but פּלּס, as the denom. of פּלס, Psalm 58:3, is not connected with all the places where the verb is united with the obj. of the way, and Psalm 78:50 shows that it has there the meaning to break though, to open a way (from פל, to split, cf. Talmudic מפלּשׁ, opened, accessible, from פלשׁ, Syriac pelaa, perfodere, fodiendo viam, aditum sibi aperire). The opening of the way is here not, as at Isaiah 26:7, conceived of as the setting aside of the hindrances in the way of him who walks, but generally as making walking in the way possible: man can take no step in any direction without God; and that not only does not exempt him from moral responsibility, but the consciousness of this is rather for the first time rightly quickened by the consciousness of being encompassed on every side by the knowledge and the power of God. The dissuasion of Proverbs 5:20 is thus in Proverbs 5:21 grounded in the fact, that man at every stage and step of his journey is observed and encompassed by God: it is impossible for him to escape from the knowledge of God or from dependence on Him. Thus opening all the paths of man, He has also appointed to the way of sin the punishment with which it corrects itself: "his sins lay hold of him, the evil-doer." The suffix יו does not refer to אישׁ of Proverbs 5:21, where every one without exception and without distinction is meant, but it relates to the obj. following, the evil-doer, namely, as the explanatory permutative annexed to the "him" according to the scheme, Exodus 2:6; the permutative is distinguished from the apposition by this, that the latter is a forethought explanation which heightens the understanding of the subject, while the former is an explanation afterwards brought in which guards against a misunderstanding. The same construction, Proverbs 14:13, belonging to the syntaxis ornata in the old Hebrew, has become common in the Aramaic and in the modern Hebrew. Instead of ילכּדוּהוּ (Proverbs 5:22), the poet uses poetically ילכּדנו; the interposed נ may belong to the emphatic ground-form ילכּדוּן, but is epenthetic if one compares forms such as קבנו (R. קב), Numbers 23:13 (cf. p. 73). The חמּאתו governed by חבלי, laquei (חבלי, tormina), is either gen. exeg.: bands which consist in his sin, or gen. subj.: bands which his sin unites, or better, gen. possess.: bands which his sin brings with it. By these bands he will be held fast, and so will die: he (הוּא referring to the person described) will die in insubordination (Symm. δι ̓ ἀπαιδευσίαν), or better, since אין and רב are placed in contrast: in want of correction. With the ישׁגּה (Proverbs 5:23), repeated purposely from Proverbs 5:20, there is connected the idea of the overthrow which is certain to overtake the infatuated man. In Proverbs 5:20 the sense of moral error began already to connect itself with this verb. אוּלת is the right name of unrestrained lust of the flesh. אולת is connected with אוּל, the belly; אול, Arab. âl, to draw together, to condense, to thicken (Isaiah, p. 424). Dummheit (stupidity) and the Old-Norse dumba, darkness, are in their roots related to each other. Also in the Semitic the words for blackness and darkness are derived from roots meaning condensation. אויל is the mind made thick, darkened, and become like crude matter.