Charles Ellicott Commentary Proverbs 15:21

"Folly is joy to him that is void of wisdom; But a man of understanding maketh straight his going." — Proverbs 15:21 (ASV)

Folly. Shown in wasted opportunities, and the commission of evil (Proverbs 10:23), while the “man of understanding” directs his way in accordance with the will of God.