Is it possible to make a decision having all of the facts? And if not, what causes us to make a decision?
Technically, sure. I might decide what I'm eating for lunch today, constraining myself to whatever is in the pantry. I look in the pantry, I have the facts, I make a decision.
But the larger decisions are never driven by 'facts' alone. I changed jobs last year. The factual part of the decision making was around money. I was comparing multiple offers, and that was a common measure of which offer was 'better'. Even then, it was hard to align, due to bonus schemes, moving costs (multiple offers were overseas) and the like.
But that was as close to a fact-based measure as I had. Everything else was subjective. Which workplace seemed to best fit my personality? What would a 'normal' day look like in each role? How would my family adjust to moving overseas? How would my family adjust to not being able to move overseas (I moved to a local company, rather than an international). Which business offered a better career path? Would I need to manage people? What sort of people were they?
I mean...you get the idea. Almost NOTHING in that decision making process was factual to me, and I certainly didn't take the one offering the most money, which was the one clear fact.
In terms of how we make a decision...well...this is very ballpark, but...
1) I tend to think of things in terms of cognitive dissonance, but you can look at it as a change agent or whatever. There is something which results in a decision needing to be made. In my case, I was dissatisfied with certain aspects of my current job (not everything, by any means) so I started to at least casually consider options.
2) As part of that process, I gathered as much information as I could. Most of that information was subjective, anecdotal, or what might be called 'gut-feel'. Some was also reactionary. (as in 'Well, working for a large multinational is frustrating me due to administrative tasks...going to a smaller local business might reduce that burden'. I had no real idea if it would.)
3) Subjectively, I made a decision. I wanted to move, was the first. And of the choices I had, what was choice A, and what parameters would lead me to actually follow through? (in my case this was things like money, family's blessing, etc)
4) I ended up changing my mind based on some of the details which came to life, and went to Plan B. So far seems to have turned out pretty well. Hard to look at all this as a fact-based decision making process though.