Some people have learned to get by on very little sleep and stay alert for hours without getting tired. Others have learned to run across thin ropes, even when they're slanted. People can carry enormous weights that seem beyond human ability. They can dive to incredible depths and hold their breath underwater for amazing lengths of time. There are countless other examples where practice has overcome every obstacle. They prove that nothing is too difficult when your mind is set on enduring it.
Some, who are satisfied with short hours of rest, have learned to watch for long periods without weariness. Men have learned to run upon the thinnest ropes even when slanting, to carry huge burdens, scarcely within the compass of human strength, or to dive to enormous depths and suffer themselves to remain under the sea without any chance of drawing breath. There are a thousand other instances in which application has conquered all obstacles, and proved that nothing which the mind has set itself to endure is difficult.