Aus der Aufklärung
Not the truth in whose possession some human being is, or thinks he is, but the honest trouble he has taken to get behind the truth is what constitutes the worth of a human being. For it is not through the possession but through the search for truth that his powers expand, and in this alone consists his ever growing perfection. Possession makes tranquil, indolent and proud.
If God held in his closed right fist all truth and in his left hand only the ever live drive for truth, albeit with the addition that I should always and evermore err, and he said to me, Choose! I should humbly grab his left hand, saying, Father, give! Pure truth is after all for you alone!
-- Gotthold Ephraim Lessing, 1778
A very popular error: having the courage of one's convictions; rather it is a matter of having the courage for an attack on one's convictions!!!
-- Friedrich Nietzsche, 1887
You can be certain, and be wrong.
-- John Kerry, 2004
All right, not quite so poetic, that last one, but the point remains something like the same. If only he had the courage for a real attack on someone else's convictions.