He that begetteth a fool doth it to his sorrow,.... As it proves in the issue; though it was joy to him when a man child was born, and took delight in him while in infancy and childhood, and promised himself much happiness in him when at years of discretion; but, instead of that, he departs from his education principles, despises all parental counsels and advice, and goes into all the extravagance of sin and folly; which is an heartbreaking to his godly and religious parents; for this is to be understood; not of an idiot, but of a wicked son, taking bad courses;
and the father of a fool hath no joy; in his son, but sorrow, and has scarce any joy or pleasure in anything else in all his enjoyments; the trouble he is filled with on his account embitters all he has, that he can take no satisfaction, or have any comfort of life; the concern for his son is uppermost in his thoughts, and hinders him from taking that pleasure which otherwise he might enjoy.

This speaks very plainly what many wise and good men feel very strongly, how grievous it is to have a foolish, wicked child.

(Compare Proverbs 23:24). Different words are rendered by "fool," both denoting stupidity and impiety.

The first three parts of the old Solomonic Book of Proverbs ((1) Prov 10-12; (2) 13:1-15:19; (3) 15:20-17:20) are now followed by the fourth part. We recognise it as striking the same keynote as Proverbs 10:1. In Proverbs 17:21 it resounds once more, here commencing a part; there, Proverbs 10:1, beginning the second group of proverbs. The first closes, as it begins, with a proverb of the fool.
21 He that begetteth a fool, it is to his sorrow;
And the father of a fool hath no joy.
It is admissible to supply ילדו, developing itself from ילד, before לתוּגה לו (vid., regarding this passive formation, at Proverbs 10:1, cf. Proverbs 14:13), as at Isaiah 66:3, מעלה (Fl.: in maerorem sibi genuit h. e. ideo videtur genuisse ut sibi maerorem crearet); but not less admissible is it to interpret לתוגה לו as a noun-clause corresponding to the ולא־ישׂמח (thus to be written with Makkeph): it brings grief to him. According as one understands this as an expectation, or as a consequence, ילד, as at Proverbs 23:24, is rendered either qui gignit or qui genuit. With נבל, seldom occurring in the Book of Proverbs (only here and at Proverbs 17:7), כּסיל, occurring not unfrequently, is interchanged. Schultens rightly defines the latter etymologically: marcidus h. e. qui ad virtutem, pietatem, vigorem omnem vitae spiritualis medullitus emarcuit; and the former: elumbis et mollitie segnitieve fractus, the intellectually heavy and sluggish (cf. Arab. kasal, laziness; kaslân, the lazy).
(Note: Nldeke's assertion (Art. Orion in Schenkel's Bibel-Lexicon) that the Arab. kasal corresponds to the Hebr. כּשׁל proceeds from the twofold supposition, that the meaning to be lazy underlies the meaning to totter (vid., also Dietrich in Gesenius' Hebrews. Wrterbuch), and that the Hebr. ס must correspond with the Arab. š. The former supposition is untenable, the latter is far removed (cf. e.g., כּסּא and kursı̂, ספר and sifr, מסכּן and miskı̂n). The verb כּשׁל, Aram. תּקל, is unknown in the Arab.)