Stop, just for a second, and ask yourself: "When's the last time I did something I had never done before?"

Really think about it... Do you have an answer?

Back in May, I went for a run in the heat of a summer afternoon in Phoenix. The sun cooked me as I coaxed myself along a six-mile route I'd run many times before, but never in such oppressive heat. Halfway through, I became woozy, increasingly unsure I could keep lifting my feet. I slowed to a walk, feeling like I might faint and immediately my face and hands were overcome with a tingling sensation of pins and needles. I staggered along for what must have been a couple minutes until the feeling subsided, then finished running the last few miles. It was the closest I had ever been to overheating. I've gone for a thousand runs, yet I'd never pushed myself that hard. I'd never experienced anything like it before.