To hit a/the wall

Sometimes you hear someone say, or you read, "then he hit a wall" --- meaning what exactly?

Runners "hit a wall." It's a point where the runner is exhausted and in pain. But if she keeps running, the runner can go past this point. "Get a second wind."

Am I right sports fans? I have never experienced this. I've never run anywhere and my life and don't plan to.

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