The human brain simply does not have the capacity to either truly believe or disbelieve any given piece of data solely by choice. Simply cannot happen. I have often asserted that the ability to do a thing must precede the right to do it. Since no such ability exists, no right exists. Someone disagreed with me recently on that, saying that would mean that a person who has no ability to breathe on their own then doesn't have a right to breathe. No, the person does have the ability to breathe, assuming they can get access to the proper medical treatments, devices, etc., therefore they still have the right to breathe.
It is a given that no human has the ability to fly without the aid of some external device. Therefore, it is absurd to say that people have a right to fly if they want, in that context. Obviously, people do have the ability to fly with various kinds of machinery, and therefore have every right to do so.
You can take a simple test to prove my point about belief. We will assume you are looking at a computer screen at this moment. Now, try as hard as you possibly can to really believe that what you are looking at is really an elephant. Well...? Could you do it? Careful now, I didn't ask if you could imagine an elephant. I don't know whether there is such a thing as a limit to human imagination. I have not found one. But belief and imagination are entirely different critters. One guy told me that, yes, he could believe his computer screen was an elephant, and had actually done it - through the use of LSD!
Well, of course there certainly exist a number of hallucinogenic substances. But I don't think the hallucinations one has while under their effect are really controllable. But it did cause me to modify my assertion about belief to say that "normal" people (those not likely to be classified by a competent psychiatrist as suffering from delusions, etc.), under "normal" conditions (not under the influence of any chemical or electronic, etc., hallucinatory mechanisms) cannot believe a thing by choice. It doesn't matter whether we're talking about something concrete, such as whether the chair you're on really exists, or a "philosophical" question, like whether a god exists, or life after death, etc. Whatever beliefs one has are formed through the person's total life experience to date, as well as mental capacity. I would include in that, things like educational level (not necessarily formal education though).
Let's try an example. You can hear some people say they firmly believe there is life on other planets, and others will say they firmly believe there is no life anywhere but earth. Who's right? What do YOU believe on that question? Well, let's look at the facts - that's typically the best place to start!
So what is the basis for saying there is no life anywhere but earth? I know of no rational basis for this. It's a pretty certain bet that a person who would assert that is either very poorly educated, or religious, or both.
What is the basis for saying there is life elsewhere? Well, aside from the facts mentioned above, there is the fact that nowhere in nature do you ever find just one of anything. There is not just one star, or tree, or person, or galaxy, etc. So it would seem that since there is at least one planet in the universe with life on it, it is likely there are more. The bottom line on this question is, all available evidence indicates it is much more probable that there is life elsewhere than not. But it is important to not assert that there is in a dogmatic fashion, because until there is actual confirmation of life elsewhere, the possibility still exists that this is the only planet in the universe with life on it.
The point is that beliefs are not things that we pick and choose as though they were items arranged on a buffet. In one sense, beliefs "happen" to us, that is, as I said above, they form on the basis of total experience, mental capacity, etc. They can be changed though. Generally speaking, what will change a belief is additional information. In day to day life, this works fine for almost everyone. But when considering the so-called "big questions" of life - origin of the universe, god's existence, an "afterlife," etc. - it may well require more than that. Typically, people have had drummed into their heads as children whatever religious, political, and social dogmas their parents hold. Things instilled at an early age, and repeatedly reinforced for years, can be very difficult to dislodge. Perhaps the most pernicious of such dogmas (combined with most peoples' apparently innate inclination toward it) is the idea that "faith" is a valid way of acquiring knowledge. It is this more than anything, I think, that serves to keep people of all sorts in bondage to the most bizarre ideologies in religion and politics, etc.