From The Screwtape Letters—a fictional work written from a senior demon’s perspective, advising a junior tempter.

It is therefore possible to lose as much as we gain by making your man a coward; he may learn too much about himself! There is, of course, always the chance, not of chloroforming the shame, but of aggravating it and producing Despair. This would be a great triumph. It would show that he had believed in, and accepted, the Enemy’s forgiveness of his other sins only because he himself did not fully feel their sinfulness—that in respect of the one vice which he really understands in its full depth of dishonour he cannot seek, nor credit, the Mercy. But I fear you have already let him get too far in the Enemy’s school, and he knows that Despair is a greater sin than any of the sins which provoke it.

As to the actual technique of temptations to cowardice, not much need be said. The main point is that precautions have a tendency to increase fear. The precautions publicly enjoined on your patient, however, soon become a matter of routine and this effect disappears. What you must do is to keep running in his mind (side by side with the conscious intention of doing his duty) the vague idea of all sorts of things he can do or not do, inside the framework of the duty, which seem to make him a little safer. Get his mind off the simple rule (I’ve got to stay here and do so-and-so’) into a series of imaginary life lines (‘If A happened—though I very much hope it won’t—I could do B—and if the worst came to the worst, I could always do C’). Superstitions, if not recognised as such, can be awakened. The point is to keep him feeling that he has some-thing, other than the Enemy and courage the Enemy supplies, to fall back on, so that what was intended to be a total commitment to duty becomes honeycombed all through with little unconscious reservations. By building up a series of imaginary expedients to prevent ‘the worst coming to the worst’ you may produce, at that level of his will which he is not aware of, a determination that the worst shall not come to the worst. Then, at the moment of real terror, rush it out into his nerves and muscles and you may get the fatal act done before he knows what you’re about. For remember, the act of cowardice is all that matters; the emotion of fear is, in itself, no sin and, though we enjoy it, does us no good,

The Screwtape Letters
C. S. Lewis