There are those who challenge every pre-known answer and belief. They don’t accept any belief or thought before going through it over and over again, testing it, reviewing it, and maybe, only maybe they accept it.
On the other hand, there are those who are looking for actual, defined, clear answers for their questions. If there is an answer known, and if it seems good enough, that would be it, the answer, the belief, end of story.
Doubt by definition is the status between belief and disbelief. Many developments in different fields come from doubt. Almost all science was motivated by doubt. The amazing thing about doubt is that it has the capacity of growing and transmitting to everything. The “disease of doubt” is actually a state of excessive doubt, better known as obsessive-compulsive disorder.
I think as much as it depends on different personalities how much one questions the popular beliefs, it very much depends on how one is trained to look at the daily problems of life. If one is trained as an engineer, it is very likely that they are more comfortable accepting a belief, and sticking to it. However, most of the scientists, specially those involved in natural sciences, are very much in doubt, for every defined answer out there... “there could be another special condition that changes the answer”.
Now the paradox sometimes is that even if you go by methodic doubt, which is questioning a pre-accepted belief and constructing or denying it, the result depends on whether or not you want to get to your belief or not. The most famous doubt of Descart was actually doubt in himself, and he proved that he existed (“I think, therefore I am”), which is in the favored direction as toward proving his existence, even though any of his reasonings to methodic doubt could well prove that maybe he does not even exist.
The first one is briefly that believing what we thought were true, could be merely our minds deceiving us. Second one (my favorite) is that there was no reliable way of distinguishing when one is awake or dreaming (the same idea as you see in “Matrix”). Also his third reasoning is that there could be some demon out there that had conceived us, preventing us from judging correctly.
As far as I know, using merely the brain, makes it impossible to get to any sort of belief. As any of the methodic doubts can prove that even your existance is not certain, let alone the world, your life, and all other thoughts and beliefs. Well, when I get here, it scares me, although I am very much in doubt for every known answer in the world, but sometimes I feel I should just let it go…or maybe we need more than the rational mind; a piece of heart, a bit of soul, or some spirit is also needed to build some believing pillars for one’s ideology in life. Everyone needs some personal principles.