The use of pain from debilitating injury in life-or-death situations is completely unreliable because everyone’s pain tolerance is different and completely unpredictable. Some people will quit, some will overcome, and others will shrug it off as if nothing happened.

In the absence of debilitating injury, pain is really just asking the other person to capitulate. If they do quit, they really weren’t a threat. It’s the ones who won’t stop until they can’t think or move that are dangerous, the ones who won’t quit no matter how many times you ask them to.

Debilitating injury, on the other hand, works on everyone in equal measure.

It shuts down those who are shocked at how much it hurts and takes away vital function from both the physical lightweight and tough guy. So even though he’s not feeling that broken ankle he sure as hell can’t walk on it. Or breathe through a crushed throat. Or see through a ruined eye.

No one can take true injury — the destruction of important anatomy — and there’s no way to condition oneself against it. If there were, we wouldn’t see these things in professional sport, where the players are the epitome of bigger, faster, stronger, general toughness, conditioning and physical prowess. But that’s exactly where we do see game-ending injuries in the accidental collisions of people-on-people and people against the planet.

You can’t learn how to “take” a debilitating injury. You can learn how to take a punch.

The first step is one of experience: You have to have these things happen to you to learn that even though they suck, you can still keep going.

That first one’s always a shock, whether it’s a bloodying punch to the face or a knockdown that you can feel in your back teeth. (I can still remember the first time I got the wind knocked out of me. Utterly startling and panic inducing.) But the next time is less traumatic, and the time after that, even less so until such things would become almost laughable if they weren’t so messy and hard on your clothes.

The next step is physical conditioning — the better shape you’re in, the more resilient you’re going to be when it comes to bumps and bruises.

This is why professional boxers can weather storms of blows, any one of which would lay out your average couch-surfer. Through physical experience, they’ve not only learned how to minimize the impacts but also have built the mental toughness necessary to push through simple pain and fatigue, to keep going as long as they can think and move.

Of course, true injury cuts right through this, whether something as common as a KO from a concussion or as esoteric as incapacity from a solid liver shot. No amount of mental or physical toughness can help you there.

These initial lessons can really only be learned through happenstance and accident. We live in a physical world. And we can only learn the rules — and our own limitations — through physical engagement with this world. Nothing is as instructive or illuminating as coming up against your limitations, roughly, and having them give way to your will. And there’s only one way to experience that: in the real world.