Have you heard you’re the average of the five people with whom you spend the most time?

Yeah, me too. Turns out you can find lots of studies on how people influence you, from how happy you are to how much you weigh to how much money you make. It’s not as simple as a “law of averages,” but the general sentiment of how much your environment impacts you is the big...

“Good, every year we’ll get 52 more practices than each of your competitors.”

This is what Michael Phelps’ coach told him when Phelps committed to doing workouts on Sundays. If he could do the work when others weren’t, it would give him a decisive advantage in the upcoming competitions.

It worked. Phelps is the most decorated Olympian of all time. Not...