Here diligence is opposed, not to sloth but to haste. Undue hurry is as fatal to success as undue procrastination.

The thoughts of the diligent [tend] only to plenteousness; but of (c) every one [that is] hasty only to want.
(c) He who goes rashly about his business and without counsel.

The thoughts of the diligent tend only to plenteousness,.... A man that is thoughtful and studious, and wisely forms schemes in his mind, and diligently pursues them; the issue of it is, generally speaking, prosperity and plenty: such a man is usually thriving and flourishing; and this holds good in things spiritual, as well as in things temporal, Matthew 25:29;
but of everyone that is hasty only to want; that is in haste to be rich, and is resolved to be so, right or wrong, he comes at last to poverty and want: or he who is rash and precipitate in acting, who never thinks before he acts, but rashly engages in an affair; or, however, does not give himself time enough to think it over, but, as soon as ever it has entered his thoughts, he immediately attempts to put it in execution; a man so thoughtless and inconsiderate, so rash and hasty, brings himself and family to poverty; see Proverbs 20:21.

The really diligent employ foresight as well as labour.

The contrast is between steady industry and rashness (compare Proverbs 19:2).

5 The striving of the diligent is only to advantage.
And hastening all [excessive haste] only to loss;
or in other words, and agreeably to the Hebrews. construction:
The thoughts of the industrious are (reach) only to gain,
And every one who hastens - it (this his hastening) is only to loss.
Vid., at Proverbs 17:21. At Proverbs 10:4, Luther translates "the hand of the diligent," here "the plans of an expert [endelichen]," i.e., of one actively striving (Proverbs 22:29, endelich = מהיר) to the end. The אץ, hastening overmuch, is contrasted with the diligent: Luther well: but he who is altogether too precipitant. Everywhere else in the Proverbs אץ has a closer definition with it, wherefore Hitzig reads אצר, which must mean: he who collects together; but אץ along with חרוץ is perfectly distinct. The thought is the same as our "eile mit Weile" [= festina lente], and Goethe's
Wie das Gestirn ohne Hast,
Aber ohne Rast
Drehe sich jeder
Um die eigne Last.
"Like the stars, without haste but without rest, let every one carry about his own burden," viz., of his calling that lies upon him. The fundamental meaning of אוץ is to throng, to urge (Exodus 5:13), here of impatient and inconsiderate rashness. While on the side of the diligent there is nothing but gain, such haste brings only loss; over-exertion does injury, and the work will want care, circumspection, and thoroughness. In the Book of Proverbs, the contrasts "gain" and "loss" frequently occur, Proverbs 11:24; Proverbs 14:23; Proverbs 22:16 : profit (the increase of capital by interest), opp. loss (of capital, or of part thereof), as commercial terms.

Hasty - Who manages his affairs rashly.