“Permanence, perseverance and persistence in spite of all obstacles, discouragements, and impossibilities: It is this, that in all things distinguishes the strong soul from the weak.”

The Light of the Soul: Its Science and Effect: a paraphrase of the Yoga Sutras of Patanjali, with commentary (1927)

1964 Memorial Edition, p. 266 http://www.jfklibrary.org/Research/Research-Aids/Ready-Reference/JFK-Quotations/Profiles-in-Courage-quotations.aspx
Variant: A man does what he must — in spite of personal consequences, in spite of obstacles and dangers and pressures — and that is the basis of all human morality.
Source: Pre-1960, Profiles in Courage (1956)
Context: The courage of life is often a less dramatic spectacle than the courage of a final moment; but it is no less a magnificent mixture of triumph and tragedy. A man does what he must — in spite of personal consequences, in spite of obstacles and dangers, and pressures — and that is the basis of all human morality. In whatever area in life one may meet the challenges of courage, whatever may be the sacrifices he faces if he follows his conscience — the loss of his friends, his fortune, his contentment, even the esteem of his fellow men — each man must decide for himself the course he will follow. The stories of past courage can define that ingredient — they can teach, they can offer hope, they can provide inspiration. But they cannot supply courage itself. For this each man must look into his own soul.
Context: For without belittling the courage with which men have died, we should not forget those acts of courage with which men — such as the subjects of this book — have lived. The courage of life is often a less dramatic spectacle than the courage of a final moment; but it is no less a magnificent mixture of triumph and tragedy. A man does what he must — in spite of personal consequences, in spite of obstacles and dangers, and pressures — and that is the basis of all human morality. In whatever area in life one may meet the challenges of courage, whatever may be the sacrifices he faces if he follows his conscience — the loss of his friends, his fortune, his contentment, even the esteem of his fellow men — each man must decide for himself the course he will follow. The stories of past courage can define that ingredient — they can teach, they can offer hope, they can provide inspiration. But they cannot supply courage itself. For this each man must look into his own soul.

Still Me (1999); also quoted at the Christopher Reeve Foundation http://www.christopherreeve.org/site/c.geIMLPOpGjF/b.1097025/k.6FF5/Christopher_and_Dana_Reeve.htm
Context: When the first Superman movie came out, I gave dozens of interviews to promote it. The most frequent question was: What is a hero? My answer was that a hero is someone who commits a courageous action without considering the consequences. Now my definition is completely different. I think a hero is an ordinary individual who finds the strength to persevere and endure in spite of overwhelming obstacles. They are the real heroes, and so are the families and friends who have stood by them.

Source: The Italian Duke's Virgin Mistress

1960s, Review of Teilhard de Chardin's "The Phenomenon of Man", 1961