“A genius is not very likely to ever discover himself; neither is he very likely to be discovered by his intimates; in fact I think I may put it in stronger words and say it is impossible that a genius—at least a literary genius—can ever be discovered by his intimates; they are so close to him that he is out of focus to them and they can't get at his proportions; they cannot perceive that there is any considerable difference between his bulk and their own. They can't get a perspective on him, and it is only by a perspective that the difference between him and the rest of their limited circle can be perceived. St. Peter's cannot be impressive for size to a person who has always seen it close at hand and has never been outside of Rome; it is only the stranger, approaching from far away in the Campania, who sees Rome as an indistinct and characterless blur, with the mighty cathedral standing up out of it all lonely and unfellowed in its majesty. Thousands of geniuses live and die undiscovered—either by themselves or by others. But for the Civil War, Lincoln and Grant and Sherman and Sheridan would not have been discovered, nor have risen into notice.”

Source: Autobiography of Mark Twain, Vol. 3 (2015), pp. 57–58