“Let us be wary of ready-made ideas about cowardice and courage: the same burden weighs infinitely more heavily on some shoulders than on others.”

Rien ne pèse tant qu'un secret.
Book VIII (1678-1679), fable 6.
Fables (1668–1679)
Variant: Nothing weighs more than a secret.

1960s, The American Promise (1965)

[Naravane, Vishwanath S., Sarojini Naidu: An Introduction to Her Life, Work and Poetry, http://books.google.com/books?id=h6v8HsRUBucC&pg=PA133, 1 January 1996, Orient Blackswan, 978-81-250-0931-3, 133–]

Source: And the Mountains Echoed

As quoted by Sir William Osler in his introduction to The Life of Pasteur (1907) by Rene Vallery-Radot, as translated by R .L. Devonshire (1923)
Discours de réception de Louis Pasteur (1882)
Context: He who proclaims the existence of the Infinite, and none can avoid it — accumulates in that affirmation more of the supernatural than is to be found in all the miracles of all the religions; for the notion of the Infinite presents that double character that forces itself upon us and yet is incomprehensible. When this notion seizes upon our understanding we can but kneel... I see everywhere the inevitable expression of the Infinite in the world; through it the supernatural is at the bottom of every heart. The idea of God is a form of the idea of the Infinite. As long as the mystery of the infinite weighs on human thought, temples will be erected for the worship of the Infinite, whether God is called Brahma, Allah, Jehovah, or Jesus; and on the pavement of these temples, men will be seen kneeling, prostrated, annihilated by the thought of the Infinite.

Source: Solaris (1961), Ch. 11: "The Thinkers", p. 158

Looking for an Honest Man (2009)
Context: With his attractive picture of human flourishing, Aristotle offers lasting refuge against the seas of moral relativism. Taking us on a tour of the museum of the virtues — from courage and moderation, through liberality, magnificence, greatness of soul, ambition, and gentleness, to the social virtues of friendliness, truthfulness, and wit — and displaying each of their portraits as a mean between two corresponding vices, ­Aristotle gives us direct and immediate experience in seeing the humanly beautiful. Anyone who cannot see that courage is more beautiful than cowardice or rashness, or that liberality is more beautiful than miserliness or prodigality, suffers, one might say, from the moral equivalent of color-blindness.