There's a moment in every hard effort where your body files a formal complaint. The legs go quiet. The lungs get loud. Some small, reasonable voice suggests that this would be a fine place to stop.
That moment is the whole thing. Not the finish, not the medal, not the number on the watch — the moment you decide whether the complaint gets a vote. Suffering well isn't about not feeling it. It's about feeling all of it and choosing to stay one beat longer.
The redline isn't a wall you crash into. It's a line you walk up to, deliberately, and then step over because you decided beforehand that you would. The mark we stitch onto everything we make is exactly that: a heartbeat climbing, hitting the ceiling, and cresting past it.
You will not always win the argument with the reasonable voice. But you can get better at having it. That's the practice. That's the point.
You don't drift to your redline. You choose it, and then you choose it again.