Nietzsche published his book, and was at once pronounced crazy by the world -- by a world which included tens of thousands of bright, sane men who believed exactly as Nietzsche believes, but concealed the fact, and scoffed at Nietzsche. What a coward every man is! and how surely he will find it out if he will just let other people alone and sit down and examine himself. The human race is a race of cowards; and I am not only marching in that procession but carrying a banner.
- Autobiography of Mark Twain, Volume 3 (2015)

There are several good protections against temptation, but the surest is cowardice.
- "Pudd'nhead Wilson's New Calendar"

We all live in the protection of certain cowardices which we call our principles.
- More Maxims of Mark, Merle Johnson, 1927

You are a coward when you even seem to have backed down from a thing you openly set out to do.
- Mark Twain's Notebook