Matthew Henry Commentary Proverbs 24:17-18

"Rejoice not when thine enemy falleth, And let not thy heart be glad when he is overthrown; Lest Jehovah see it, and it displease him, And he turn away his wrath from him." — Proverbs 24:17-18 (ASV)

The pleasure we are inclined to take in the troubles of an enemy is forbidden.