“His conviction that everything happened for a reason, and would come to good, gave him laughing equanimity even in hard times.”

Source: The Ship that Flew (1939), Ch. 1 : The Magic Begins

Variant: Everything happens for a reason, even when we are not wise enough to see it. When there is no struggle, there is no strength.

Source: The Tales of Alvin Maker, Alvin Journeyman (1995), Chapter 14.

Source: 21st Century, Robert Rauschenberg, Works, Writings and Interviews, 2006, p. 71

Rome, or Reason? A Reply to Cardinal Manning. Part I. The North American Review (1888)
Context: Among the “some two hundred and fifty-eight” Vicars of Christ there were probably some good men. This would have happened even if the intention had been to get all bad men, for the reason that man reaches perfection neither in good nor in evil; but if they were selected by Christ himself, if they were selected by a church with a divine origin and under divine guidance, then there is no way to account for the selection of a bad one. If one hypocrite was duly elected pope—one murderer, one strangler, one starver—this demonstrates that all the popes were selected by men, and by men only, and that the claim of divine guidance is born of zeal and uttered without knowledge.

Source: 1840s, Essays: First Series (1841), Self-Reliance

"The Art of Living", interview with journalist Gordon Young first published in 1960
Variant: [T]here are as many nights as days, and the one is just as long as the other in the year's course. Even a happy life cannot be without a measure of darkness, and the word "happy" would lose its meaning if it were not balanced by sadness.