C. F. Keil and Franz Delitzsch on Proverbs 4:16

Pro 4:16

In the reason here given the perf. may stand in the conditional clauses as well as in Virgil’s Et si non aliqua nocuisses, mortuus esses; but the fut., as in Ecc 5:11, denotes that they (the רעים and the רשׁעים) cannot sleep, and are deprived of their sleep, unless they are continually doing evil and bringing others into misery; the interruption of this course of conduct, which has become to them like a second nature, would be as the interruption of their diet, which makes them ill. For the Kal יכשׁולוּ, which here must have the meaning of the person sinning (cf. Pro 4:19), and would be feeble if used of the confirmed transgressors, the Kerı̂ rightly substitutes the Hiphil יכשׁילוּ, which occurs also 2Ch 25:8, there without an object, in the meaning to cause to fall, as the contrast of עזר (to help).