Greatness is not a teachable nor gainable thing, but the expression of the mind of a God-made man: teach, or preach, or labour as you will, everlasting difference is set between one man's capacity and another's; and this God-given supremacy is the priceless thing, always just as rare in the world at one time as another.... And nearly the best thing that men can generally do is to set themselves, not to the attainment, but the discovery of this: learning to know gold, when we see it, from iron-glance, and diamond from flint-sand, being for most of us a more profitable employment than trying to make diamonds of our own charcoal. [ John Ruskin ]