“What difference would it make” is at the core of his philosophy, which was practical, or pragmatic, in its concern for what the consequences of a belief are rather than what its truth is. That is to say, most philosophy is geared toward finding out the existing condition of things. James focused instead on how beliefs shape the world. Rather than ask whether or not God existed, James might try to ascertain what difference belief in God would make to how you live your life or how a society conducts itself. What is the consequence of the belief, rather than the truth of it? It is a deeply American approach, directed toward the malleability rather than the immutability of the world, toward what we make of it, rather than what it is made of. This aspect of Jame’s philosophy is sometimes misinterpreted as a kind of easy solipsism akin to the contemporary New Age motion that we each create our reality (a crass way of overlooking culture, politics, and economics — that is, realities are made, but by groups, movements, ideologies, religions, societies, economics, and more, as well as natural forces, over long stretches of time, not by individuals alone).
Rebecca Solnit, A Paradise Built in Hell: The Extraordinary Communities That Arise in Disasters, 2009