William McRavenwas, commander of US Special Force Command, gave an oft-quoted speech at a university graduation in Texas in 2014. He spoke of his experiences in becoming a US Navy SEAL. SEAL training is regarded as being the toughest in the world. McRaven spoke about his Hell Week at Basic Underwater Demolition SEAL (BUD/S) training:

The ninth week of SEAL training is referred to as Hell Week. It is six days of no sleep, constant physical and mental harassment and one special day at the Mud Flats. The Mud Flats are an area between San Diego and Tijuana where the water runs off and creates the Tijuana sloughs—a swampy patch of terrain where the mud will engulf you. You paddle down to the mud flats and spend the next 15 hours trying to survive the freezing-cold mud, the howling wind and the incessant pressure from the instructors to quit.

As the sun began to set that Wednesday evening, my training class was ordered into the mud. The mud consumed each man till there was nothing visible but our heads. The instructors told us we could leave the mud if only five men would quit—just five men and we could get out of the oppressive cold.

Looking around the mud flat, it was apparent that some students were about to give up. It was still over eight hours till the sun came up—eight more hours of bone-chilling cold. The chattering teeth and shivering moans of the trainees were so loud it was hard to hear anything. And then, one voice began to echo through the night—one voice raised in song.

The song was terribly out of tune, but sung with great enthusiasm. One voice became two, and two became three, and before long everyone in the class was singing.

We knew that if one man could rise above the misery then others could as well. The instructors threatened us with more time in the mud if we kept up the singing—but the singing persisted. And somehow, the mud seemed a little warmer, the wind a little tamer and the dawn not so far away.