All of us accept as "fact" assertions for which we individually have only limited evidence -- and in many cases, people are not completely aware of all the assumptions they make as they navigate through daily life
I agree. I'm of the belief that we actually can know extremely little, as knowledge assumes truth and, consequently, it is impossible to know something that is false. Do I "know" that my father is not actually an undercover CIA agent? Do I "know" that I'm not dreaming? Do I "know" that there is not a murderer directly behind me with a very large knife? No on all counts. I have very good reason to believe that none of these things are the case, and I operate (as you imply) on the assumption that these things are false. Those are rather silly examples, but the notion of knowledge and what we can and cannot know applies to pretty much everything that we do. It would be pretty much impossible for us to operate solely on knowledge and not to make certain assumptions about the world we live in and the people we deal with.
How we really form our own various "beliefs" -- about what is "real" and what is "illusory", about our political or economic systems, about proper ways to interact with others, about how we should spend our money or time or lives &c&c -- may be obscure
I think "may" is an understatement - hence it's a good question to ask.
In my experience, it is very uncommon for people to change their "beliefs," even long after I have convinced myself that I have brilliantly out-argued them on all the key points. Looking around, I suspect my own experience is not unique in this respect.
I suspect that there is a reason for this. I look at basic beliefs (or not so basic if you prefer, but the semantics are unimportant), such as religion or political affiliation. I tend to think that these foundational beliefs lay the groundwork for more beliefs to be accepted by an individual. Over the years, people build a chunk of their self-image on these beliefs. They begin to define themselves in such a respect. As such, if they were to relinquish any of the beliefs on which others are based, then their self-image might take a hit - even a pretty big one. So I think there's a vested interest in people hanging onto their beliefs, come hell or high water, lest their worldview is dramatically altered. I hope that makes sense.
The nineteenth and twentieth centuries produced a number of thinkers claiming that we are all dishonest about how our convictions actually arise: Nietzsche, for example, pointed out that many ideas most of us hold, we hold simply because we want to fit into the social groups around us; Marx produced an political-economic analysis that was concerned with how social groups protect their own interests and reproduce their group structures, by a process of self-justifying their own behaviors; Freud took the view that humans are driven by instinctual needs, which they have learned (through their own particular individual histories) to channel in certain ways and that our self-images are objectively inaccurate and mislead us.
How do people actually form their beliefs? What actually leads people to change their beliefs?
There are entire books about this very topic, and some of those books use words that are bigger than my patience threshold, so I will admit that I'm certainly not the most learned individual on this topic. But I'll be happy to supply my thoughts on the subject.
I tend to agree with evolutionists when it comes to how we originally form our beliefs. We believe what our parents tell us. It makes sense for a child to believe what their parents tell them, as typically parents only want to do right by their children and children have no reason to distrust their parents. That's a notion supported by evidence, as there is a strong correlation between things like religion and political party affiliation of children and that of the parents. That is by no means the rule, however, as the correlation is not perfect.
Those are the cases that interest me the most. The "apostates" for whatever traditional thought they were brought up with. What brings them to abandon their former beliefs? I've had experiences where I have renounced long-held beliefs, but usually not through any sort of argument. For me, the true change always came from within. For example, I used to be a Baptist. When I was younger I lost someone to suicide, and the problem of evil popped up in my head and, eventually, lead me to where I'm at today with my theological viewpoints. Now, plenty of religious people (even Baptists :) ) have experienced tremendous losses, and have undoubtedly questioned their own faith, but have not renounced it. One thing I often wonder is what separates me from them? What makes me different? That's the 64,000 dollar question, at least for me.
Lastly, there is a theory in psychology called cognitive dissonance that (1) has good empirical support and (2) can explain how we form and change our beliefs quite nicely. In a nutshell, it's a theory that states when we act in a way which is incongruent with our beliefs, we will experience mental discomfort (aka dissonance). The result of that dissonance is that we, more often than not, adjust our beliefs accordingly so that we do not experience such dissonance. It's a fairly broad theory that can encompass quite a lit, but it's something akin to what you touched on in your OP.
Hope I said something worthwhile :D