Charles Ellicott Commentary Proverbs 26:11

"As a dog that returneth to his vomit, [So is] a fool that repeateth his folly." — Proverbs 26:11 (ASV)

So a fool returneth to his folly.—Though he knows it to be folly, and ruinous to him, yet vice has become to him a second nature, and he cannot, even if he would, escape from it. This is especially true of those who have given way to drink or impurity of life.