"I absolutely cannot see how one can later make up for having failed to go to a good school at the proper time. Such a man does not know himself; he walks through life without having learned to walk; his flabby muscles reveal themselves with every step. Sometimes life is so merciful as to offer this hard schooling once more later: sickness for years perhaps, that demands the most extreme strength of will and self-sufficiency; or a sudden calamity, affecting also one's wife and child, that compels one to a form of activity that restores energy to the slack fibers and toughness to the will to live. The most desirable thing is still under all circumstances a hard discipline at the proper time, i.e., at that age at which it still makes one proud to see that much is demanded of one. For this is what distinguishes the hard school as a good school from all others: that much is demanded; and sternly demanded; that the good, even the exceptional, is demanded as the norm; that praise is rare, that indulgence is nonexistent; that blame is apportioned sharply, objectively, without regard for talent or antecedents.
One needs such a school from every point of view: that applies to the most physical as well as to the most spiritual matters; it would be fatal to desire to draw a distinction here! The same discipline makes both the good soldier and the good scholar; and looked at more closely, there is no good scholar who does not have the instincts of a good soldier in his makeup. To be able to command and also proudly to obey; to stand in the ranks, but also capable at any time of leading; to prefer danger to comfort; not to weigh the permitted and the forbidden on a shopkeeper's scales; to be a foe more of the petty, sly, parasitic, than of the evil. -- What does one learn in a hard school? Obeying and commanding."
-- Friedrich Nietzsche, The Will to Power, 912

"From the military school of life. -- What does not kill me makes me stronger."
-- Friedrich Nietzsche, Twilight of the Idols, "Maxims and Arrows," 8