He who loses wealth loses much; he who loses a friend loses more; but he that loses his courage loses all.

Money can be rebuilt, and friendships, painfully, can be repaired or replaced. Nerve is different, because it is the thing you would use to rebuild the others. Once you stop being willing to try, every other loss becomes permanent by default. That is the sense in which it sits underneath the rest.

If you are low at the moment, do not set yourself a large test. Do one small thing you have been avoiding out of apprehension, something that takes a few minutes. Courage recovers the way strength does, in repetitions too small to feel heroic.