Proverbs 26:11 Kabbalah

כְּ֭כֶלֶב שָׁ֣ב עַל־קֵא֑וֹ כְּ֝סִ֗יל שׁוֹנֶ֥ה בְאִוַּלְתּֽוֹ׃

As a dog that returneth to his vomit, So is a fool that repeateth his folly.

Read kabbalistic (mystical) interpretation of Proverbs 26:11: and classical mystical sources.