The researchers admitted that there's still a lot we don't know about how or why aerobic exercise actually affects our mood. With something as subjective as what makes people happy, it's difficult to say if any one thing will always work. But these findings suggest it wouldn't hurt to give a run a try next time you're feeling super sad. At the very least, this is good info if you have to get through watching this scene from Good Will Hunting. Dry those tears; then, lace up your running shoes.