I like this quote by Reif Larsen in The Selected Works of T.S. Spivet:
Watching his eyes, I suddenly had an idea of how adults can hold on to a feeling for very long periods of time, long after the event is finished, long after cards have been sent and apologies made and everyone else had moved on. Adults were pack rats of old, useless emotions.
It’s true for me. I generally don’t harbor grudges or things of that nature. But I do clig to negative feelings for years after something goes wrong. It’s one thing to learn a lesson from something; it’s another to continually flog yourself over it.
Being a pack rat does more harm than good.