as a dog returns to his vomit, so a fool repeats his folly
Foolish people are apt to repeat their missteps. A: "I can't believe Sarah is going skiing again, after she broke her leg the last time." B: "Well, as a dog returns to his vomit, so a fool repeats his folly."
1. To be discharged forcefully and abundantly; spew or gush: The dam burst, and the floodwaters vomited forth.
2. To eject or discharge something in a gush; spew something out: The volcano vomited forth lava and ash. The belly of the ship opened and vomited the cargo forth.