One of the hardest things to do is believe in something all the way. This is true of reality, religion, life, relationships, and alternative medical treatments. Many things are partly true, with their opposites often equally true. Most human motivations are dazzlingly mixed.

Choosing things and people to believe in is a dicey business — one conducted largely unconsciously, in realms where we’re easily misled by our habit-bound ways of perceiving and thinking about the world, our fears and desires. To believe in something freely and accurately, you first have to see it clearly, and that is nearly impossible for us to do.

We see things through the filter of who we are, which means we see them partially and with prejudice. There is no other way for us to see them. This is why Uchiyama Roshi observed that when a person dies, an entire world dies with her: the unique world construed by that person, believed in by her.

I’m thinking now of a particular kind of belief — faith. To me, faith is not imperviousness to “the facts,” those elusive entities more often cited than proved. Faith is a decision in the absence of conclusive evidence. This poverty of proof is our usual circumstance, with the things that matter most to us often least susceptible to being proven.

How we cope with the unknown that is our lives, which beliefs we choose, exert great influence over our experience: what happens to us and how we feel about it. We know of the placebo effect, when faith in a treatment makes it work. Such faith is powerful and common enough to pose a challenge to find drugs that outperform it. Its opposite, the nocebo effect, is equally powerful, although its mechanisms are less well understood medically.

Carl Jung wrote that when one finds oneself with a question whose answer cannot be proven one way or the other, one should select whichever belief is most helpful. Advice both pragmatic and idealistic, one of my favorite combinations.

The time to believe in something all the way is for as long as you’re doing it. Or living it or loving it. If what you do, live, or love turns out to be unhelpful, you can always change your beliefs and actions based on your experience — something we’d benefit from doing more often. But hedging faith hinders the unknown’s ability to help, and to prove itself. The only way to give an unknown a fair chance is to believe in it with all your heart.