Every successful man or great genius has three particular qualities in common. The most conspicuous of these is that they all produce a prodigious amount of work. The second is that they never know fatigue. And the third is that their minds grow more brilliant as they grow older, instead of less brilliant. Great men's lives begin at forty, where the mediocre man's life ends. The genius remains an ever-flowing fountain of creative achievement until the very last breath he draws.