- 1852, Nathaniel Hawthorne, The Blithedale Romance, Boston: Ticknor, Reed and Fields, ch. 2:
- The greatest obstacle to being heroic is the doubt whether one may not be going to prove one's self a fool; the truest heroism is, to resist the doubt; and the profoundest wisdom, to know when it ought to be resisted, and when to be obeyed.
- 1901 October, Charles Waddell Chesnutt, The Marrow of Tradition, Boston; New York: Houghton, Mifflin, page 233:
- The workings of the human heart are the profoundest mystery of the universe.
- 1994, Catherine Faber, “The Word of God” (song), Echo's Children:
- The profoundest act of worship is to try to understand.