People "believe" what seems correct to them. I've always been puzzled how so many people see belief as an action, and not a result, as it actually is.
As an exercise, it becomes clear that we cannot simply choose to believe something when presented with the decision to believe something that we cannot find true. As an example, if I say that there's an invisible dragon on my shoulder who tells me what to do, it is unlikely that I will find anyone who can decide to believe that what I say is true, and then actually, sincerely believe my claim.
Now, I think people can, over time, prime themselves for a belief through a method of cognitive behavioral modification, but it is not an instantaneous decision, and it still comes down to, eventually, the claim of belief resonating as true to them.