Imagine for a moment that a man is hiking in the Alps when he suddenly finds his progress blocked by a narrow but terrifyingly deep crevasse. There’s no safe passage around it, and he cannot retreat the way he came. The question, then, isn’t what the man should do; his only option is to leap over the chasm. The question is how he should feel about doing it.
This hypothetical scenario was devised by William James to help us think about the merits of certainty. While most of his fellow philosophers were criticizing it as intellectually untenable or morally repugnant or both, James decided to come to its defense. Or rather, to its partial defense: he, too, worried about the potential moral consequences of certainty—but, ever the pragmatist, he argued that it had also some distinct practical advantages. However intellectually honorable doubt might be, he pointed out, it would clearly serve our hypothetical hiker poorly. The better option would be for him to believe absolutely in his ability to leap over the crevasse.
James meant by this that shaky ground should not always deter us from unshakable faith. There are countless instances when our own lives or the larger world have been changed for the better by a passionate conviction: that you can lower your cholesterol or get into medical school or secure a better future for your children; that polio can be eradicated or that the wilderness can be protected or that people with disabilities should not be prevented from rich and full participation I public life. As James put it, sometimes unswerving beliefs “help to make the truth which they declare.”
– Being Wrong Adventures in the Margin of Error by Kathryn Schulz