Albert Bigelow Paine,
The Boys' Life of Mark Twain — Chapter 58
(1916)
“ Hutton, in Princeton, you said: "If a man is a pessimist before he is forty-eight, he knows too much. If he is an optimist after he is forty-eight, he knows too little." Now we know you are an optimist, and nobody would dare to accuse one on the "seven-terraced summit" of knowing little. So probably you are not seventy, after all, but only forty-seven! Helen Keller was right. Mark Twain was never a pessimist in his heart. ”
