How hard you should push yourself when chasing big dreams

Researchers, founders and executives insist that running can teach essential lessons in sticking with big goals and mental toughness.

Olympic distance runner Alexi Pappas's advice from one of her running coaches is to use the rule of thirds:

"Whenever you're chasing a big dream, you're supposed to feel good a third of the time, okay a third of the time and crappy or not great a third of the time."

"If you feel too good all the time, you're not pushing yourself enough, and if you feel too fatigued, you might be burning out."