A study was conducted in which scientists stuck a thermometer up a cheetah’s ass and made it run on a treadmill. They discovered that, no matter what they did, the cheetah refused to run once its body temperature reached 105 degrees Fahrenheit.
The big cat’s sense of self-preservation overrode attempts to compel it.
You might think that, compared to a large, predatory cat, the human animal is a poor hunter. We have thumbs, sure, but we have poor teeth and no claws. Our thin skin and low top speed make us easy targets. Humans have no natural weapons.
You would be wrong.
Humans, despite our low top speed, are actually adept runners. We have large knees, and thick connective tissue. Our tendons act like springs, storing and releasing energy. We have disproportionately large glutes, which obviate the need for a tail and allow us to run upright. This upright posture means quicker acceleration and more efficient strides. Our thin skin and multitude of sweat glands shed heat efficiently.
Over long distances, a well conditioned human can run down a horse.
Even humans have their limits. Like any other animal, we reach a point where our bodies beg to stop. However, unlike other animals, humans ignore this impulse. We push our bodies without food or water until our muscles are eaten away and our bones grow brittle. We deprive ourselves of sleep until delirium drives us mad.
There is a threshold beyond which a man must choose between pain and failure. Somewhere, beyond that threshold, lies the absolute limit of his capabilities.
Toeing that line, you realize that only you own the consequences of your choice – press on or quit. You can certainly quit in a flourish of sweat and movement, overselling your effort to save face.
But deep down, you know you quit.
There is no guilt like the guilt of a quitter. Whether you quit on the starting line, or three feet from the finish, or simply undercommitted, you still quit.
To quit is to know every day, for the rest of your life, that deep down you are inadequate.