Charles Ellicott Commentary Proverbs 24:9

"The thought of foolishness is sin; And the scoffer is an abomination to men." — Proverbs 24:9 (ASV)

The thought of foolishness is sin.— Rather, Sin is the contrivance (plotting) of self-will. Sin is the transgression of the law of God (1 John 3:4), when we desert the plain rule of duty, and plot how we can indulge our own self-will.