He who learns must suffer.
And even in our sleep, pain that cannot forget
falls drop by drop upon the heart,
and in our own despite, against our will,
comes wisdom to us
by the awful grace of God.
Source: Aeschylus. Agamemnon (The Oresteia)
, 458 BCE
Quoted by Robert F. Kennedy forty years ago, on the occasion of the death of Martin Luther King Jr.