Folly is a more dangerous enemy to the good than evil. One can protest against evil; it can be unmasked and, if need be, prevented by force. Evil always carries the seeds of its own destruction, as it makes people, at the least, uncomfortable. Against folly we have no defence. Neither protests nor force can touch it; reasoning is no use; facts that contradict personal prejudices can simply be disbelieved indeed, the fool can counter by criticizing them, and if they are undeniable, they can just be pushed aside as trivial exceptions. So the fool, as distinct from the scoundrel, is completely self-satisfied; in fact, he can easily become dangerous, as it does not take much to make him aggressive. A fool must therefore be treated more cautiously than a scoundrel; we shall never again try to convince a fool by reason, for it is both useless and dangerous.

If we are to deal adequately with folly, we must try to understand its nature. This much is certain, that it is a moral rather than an intellectual defect. There are people who are mentally agile but foolish, and people who are mentally slow but very far from foolish — a discovery that we make to our surprise as a result of particular situations. We thus get the impression that folly is likely to be, not a congenital defect, but one that is acquired in certain circumstances where people make fools of themselves or allow others to make fools of them. We notice further that this defect is less common in the unsociable and solitary than in individuals or groups that are inclined or condemned to sociability. It seems, then, that folly is a sociological rather than a psychological problem, and that it is a special form of the operation of historical circumstances: on people, a psychological by-product of definite external factors. If we look more closely, we see that any violent display of power, whether political or religious, produces an outburst of folly in a large part of mankind; indeed, this seems actually to be a psychological and sociological law: the power of some needs the folly of the others.

— Dietrich Bonhoeffer, “After Ten Years” (1943)