Rumination is when you go over the same—usually negative—thought again and again. You’re trying to work out why did it go wrong, what could you have done, and what could you do. “It’s useful if you do it once, but there’s no benefit to doing it again and again,” says David Cox, chief medical officer for mindful meditation app Headspace. Now, that still doesn’t stop us from obsessing, though, right? Here’s what you can do to put the brakes on a runaway train of thought.