Nagging, repetitive thoughts are the engine for music like Selena Gomez’s, “Back To You” and movies like Jason Segel’s Forgetting Sarah Marshall. Once the pesky feelings start, they’re hard to stop, and suppressing them just exacerbates the problem.

Instead of rejecting thoughts after they arrive, we can prevent them from getting there in the first place.

Reactive control can be particularly problematic because thoughts are self-reinforcing. People can partially preempt this process if they want to ensure that this thought comes to mind as little as possible.