Endurance, after all, is the only reason we even exist. We think of ourselves as nature's deadliest animals, but the truth is, a naked human is the biggest wimp in the wild. We have no fangs, no claws, no strength, and no speed.

Faced with the almost inescapable conclusion that it had been selling lemons, Nike shifted into make-lemonade mode. Jeff Pisciotta became head of a top-secret and seemingly impossible project: finding a way to make a buck off a naked foot.

The Tarahumara would party like this all night, then rouse themselves the next morning to face off in a running race that could last not two miles, not two hours, but two full days. According to the Mexican historian Francisco Almada, a Tarahumara champion once ran 435 miles, the equivalent of setting out for a jog in New York City and not stopping till you were closing in on Detroit.

Blaming the running injury epidemic on big, bad Nike seems too easy - but that's okay, because it's largely their fault.

You don't stop running because you get old, you get old because you stop running.

Every morning in Africa, a gazelle wakes up, it knows it must outrun the fastest lion or it will be killed. Every morning in Africa, a lion wakes up. It knows it must run faster than the slowest gazelle, or it will starve. It doesn't matter whether you're the lion or a gazelle-when the sun comes up, you'd better be running.

When it comes to mentors, you can't beat survival.