I'm going to change this a little bit in attempt to remove some of the personal whining and actually write something that might be useful. Heh, imagine that. Probably be more interesting than me whining about people who have decision making processes that I don't really understand, but I do use in my character creation. Don't worry, there is personal bits in here. I also give you a dose of healthy emo on top of your salad.
I consider one of my strengths to be creating characters quickly and, for the most part, giving them a fair amount of depth and making them interesting. One thing I do struggle with is making characters significantly different from myself, so I use a few tricks as part of the building process. A good part of that is actually coming down with a list of beliefs and preferences, but also the reasons behind those beliefs. You can get a lot out of knowing why characters have their quirks.
The main reason is a decision-making process helps flesh out a character's personality. If someone usually makes decisions based on their own point of view, then you can realize how they'll react to something new. On the other hand, if everything they do is based on some book, say Are You There God? It's Me, Margret, then knowing or creating that book will really help define a character's reactions. Naturally, people make decisions for different reasons and at different times. And putting them together can really make a complex character with some baffling traits and some honorable but annoying ones.
Let's start with a great character with flaws: me. :)
I don't use syrup.
I couldn't tell you where this came up with. Somewhere when I was 8, I suddenly announced at some unknown meal, that I didn't want to use syrup anymore. To this day, I still don't. This is an absolute baffling decision that really has no basis. I also consider it a flat character flaw since it was like someone put a post-it note on my forehead: "Doesn't use syrup."
The problem with it is you really can't do much with these type of decisions. They just are, they don't really define a character.
I don't like sauerkraut.
On the other hand, despite this being very close to the one above, this is not a flat character flaw. I know why I don't like sauerkraut. It is the one food that I really can't eat, but every few years I actually try it again to see if I like it yet. If you are curious, the first couple of times I had it, I really didn't like it and there was this one... incident at my dad's where I had to eat it and not throw up. After that, it became my one-and-only despised food.
Surprisingly, bleu cheese used to be on this list, but somewhere in the early 2003's, I had something with it and found that I actually liked it. But, not saurekraut. Not even when its only Fluffy's lovely Canadian bacon, pineapple, and sauerkraut pizza, I still can't eat it.
I consider the second quote to be a much better one for fleshing out a character. Yeah, the importance of why I don't like sauerkraut isn't going to show up in a story, but it gives a writer a framework for handling other decisions. For example, knowing why I don't like sauerkraut gives you an idea of what happened when the first cup of coffee I had was the sludge on the bottom of a camp pot in Boy Scouts. It was horrible. The second was so bitter that it could strip an engine block. Now, try to guess if I drink coffee?
MC: I'm against gay marriage since when BN and I were together, we couldn't get insurance, but the gay couples could.
Oh, woe is I. This isn't my quote, because I can't find an example where I made a statement like this. But, this is a decision that has a basis but makes a leap of intuition that I cannot comprehend. Well, I can, but I wouldn't have made it. It was from a discussion on gay marriage. She was against it since the company in question had to make an exception for gay couples because it wasn't a legally binding union but she couldn't get any because she and BN were just living together and not married. I tried to explain that if gay marriage was legal, then there wouldn't have been this exception, but its one of those things where MC doesn't want to change her mind, so she won't.
I call this a shallow decision. It has a reason, which is good for details, but it works on a basis of an immediate observation, without going into the depth of that observation. She doesn't care about the religious reasons or even the legal ramifications. Just simply on the fact she couldn't get insurance with a live-in lover where a gay couple who was not married could. That was as far as the basis for that decision was made.
Side note: I'm in favor of gay marriage, though I will probably never actually be in one. I simply want it to exist so gay couples have the same legal rights as heterosexual couples and we don't have exceptions like these. Don't care about the religious aspects. I just don't want to ever see a gay man crying in the waiting room because he can't visit his lover (family only). Or hearing the sick man's father telling the man's lover to go away, 'because he has no right to be there'. I hated that, and I never want to see it again. Love is love, I don't think physical form has anything to do with it.
Its pretty easy to build a character's beliefs on this. You just have to go with what they observe and react from there. Say someone broke into their house and stole $100, the character would make a decision based on that, not on the thief needing the money to save their life or something to that effect.
MJ: Actor is a horrible actor because of Movie.
Sadly, I hear this one a lot. You can change the actor's name and movie to just about anything, but it is still a damnation. MJ is big into those. One bad experience basically damns it forever. A good example: she used to go to the corner bakery every two days for the yummies. Every two days, she would be in my office, "wanna go?" Then one time, she found some mold on one of the pieces. Forevermore, the place was horrible and she actively tried to convince me not to go because there was mold once.
This is damnation. Its related to the decisions above it, but goes far beyond it. Judging from the reactions of this country, we do this a lot. It takes one thing to tear a person from political office. One indiscretion and they are basically ruined. It doesn't matter what good they did or bad, all that matters is that one thing.
Sometimes, you can reverse a damnation in a character, but it takes a lot of effort. On the other hand, it is really easy to see how a character would respond to their Subaru breaking down on the side of the road.
I suppose, expotential money is out. The majority has spoken.
Back to my flaws. When I was working on Balance, I wanted an abstract monetary system based on exponential numbers. Both MJ and bJ hated it with a passion. After a lot of discussion, they said "vote on it" and I had to follow the rules I set up, which is majority vote on any major disagreement. I win all ties. So, we voted and I lost. I still wanted it in, I really did, but I made a decision based on rules I made and I obeyed them. This is also related to the characters who can say "I know that someone planted that pot on you, but its against the law and I'm arresting you."
This is a decision based on an external framework. It can be something as rigid as a German legal system (which appears to be more regular than our own), to our own laws, to even belief in a book (obviously, the Bible). The rules don't have to be literal (good thing in some cases), but it is an external framework.
Now, a character who doesn't agree with them might push the rules or even break them. A good example is in Lethal Weapon 4, when Murtaugh brought the Chinese family into his house. He didn't agree with the rule, but he pushed or even broke them with an overriding decision came from a different basis.
I can't stand you, but I'll fight for your right to speak up.
This is related to the one before it as being a philosophical decision. I happen to be relatively behind free speech, even with people who don't agree with me. MC was surprised that, after an hour and a half of heated debate on a topic, I could put it aside so easily, wish her the best of days, and head out to work. But, knowing the above quote along with "don't hold on to anger" could easily show how I can set it aside and move on. I don't hold grudges, it isn't worth the energy or effort to do it. And, as a character, its pretty easy how I respond to things like having a close friend steal a couple thousand dollars from me. Or why I paid for SW's apartment and never asked for it back.
Flip a coin.
Can't decide? Get them both.
These are two things I frequently use. Mainly because when you really can't decide on something, it doesn't really matter which one you pick. In the end, it just is and there is nothing to worry about. This is kind of random, but you have those decisions on occasion. My first house was like that. I saw three houses that day of looking. I didn't like the third one, but I liked both the second and the first. So, I literally flipped a coin and bought the first one. And you know what? I was happy with the decision.
Talk to mom.
This is avoiding a decision. But, people do that. They try to avoid making one by directing it to someone else. This works better in situations of authority, but you rarely see leaders with it.
There is never one reason.
Recently, almost every decision I made has multiple reasons. And, because of my introspective nature, I can usually tell you why I made any decision and what the basis of it. Some characters only make it for a single reason ("I don't like cheese") while others need multiple points. Some weigh the risks while others just do it without caring about the conquences.
But this also reflects that you can have multiple decisions of a character. You can have someone who follows scriptures for almost every decision in their life, but is willing to kill someone for their wife (obviously not a scripture thing). But, having the ways someone makes a decision, regardless of how, can add some depth to a character and let you create someone who can respond to others instead of just following a scripted response.
One of the things I do with most characters is think about three significant events in their life. And just their decision. And why. With those three events, three decisions, and three reasons, I have a lot to work with. Most of the time, I will never tell the reader what those three events were. Like a properly designed public-key encryption, you keep your seeds private and then just let people see the results.
Well, I don't think I've ever tried to write something like this, but I hope it helps. Or at least, gives you an idea of how I do things.