C. F. Keil and Franz Delitzsch on Proverbs 21:2

Pro 21:2

The next group extends from Pro 21:2 to Pro 21:8, where it closes as it began. 2 Every way of a man is right in his own eyes;    But a weigher of hearts is Jahve.

A proverb similar to Pro 16:2 (where דּרכי, for דּרך, זך for ישׁר, רוּחות for לבּות). God is also, Pro 17:3, called a trier, בּחן, of hearts, as He is here called a weigher, תּכן. The proverb indirectly admonishes us of the duty of constant self-examination, according to the objective norm of the revealed will of God, and warns us against the self-complacency of the fool, of whom Pro 12:15 says (as Trimberg in “Renner”): “all fools live in the pleasant feeling that their life is the best,” and against the self-deception which walks in the way of death and dreams of walking in the way of life, Pro 14:12 (Pro 16:25).