I once performed physical training at seven o’clock in the morning on approximately one hour of sleep while still thoroughly acquainted with the previous evening’s alcohol. It was a remarkable demonstration of human determination, although I cannot say whether the determination belonged to me or whether my body was too confused to file a formal protest.

At that hour, ordinary men were enjoying coffee, reading newspapers, and contemplating the weather. I was apparently attempting to discover how many different ways a human skeleton could object to military exercise.

My head felt like a blacksmith had rented it for a weekend, my stomach was negotiating an armistice, and my legs were operating under the impression that they belonged to somebody else. Nevertheless, there I stood, ready for PT, dressed appropriately and displaying all the enthusiasm of a condemned man being offered a second helping of prison stew.

The instructor shouted, “MOVE!”

I moved. Not particularly well, mind you, but movement was technically achieved.

Somewhere between the jumping jacks and whatever fresh indignity followed, I began to appreciate the extraordinary resilience of the human body. It will endure almost anything, apparently, provided nobody asks it to remember what happened after midnight.

Looking back, I have learned an important lesson. We spend entirely too much time underestimating ourselves.

We imagine there are limits to what we can accomplish, when sometimes the only thing standing between us and greatness is a military instructor with a whistle and absolutely no sympathy. Don’t forget what you’re capable of.

Just don’t ask your liver to provide a character reference.