as a dog returns to his vomit, so a fool repeats his folly

Etymology
Originally from :
 * 1611, King James Version of the Bible, Book of Proverbs, 26:11
 * As a dog returneth to his vomit, so a fool returneth to his folly.
 * כְּכֶלֶב שָׁב עַל קֵאוֹ כְּסִיל שׁוֹנֶה בְאִוַּלְתּוֹ

Proverb

 * 1) Foolish people repeatedly do foolish things.