Adam Clarke on Job 20:4

Knowest thou not this of old - This is a maxim as ancient as the world; it began with the first man: A wicked man shall triumph but a short time; God will destroy the proud doer.

Since man was placed upon earth - Literally, since Adam was placed on the earth; that is, since the fall, wickedness and hypocrisy have existed; but they have never triumphed long. Thou hast lately been expressing confidence in reference to a general judgment; but such is thy character, that thou hast little reason to anticipate with any joy the decisions of that day.