So what is a person? What makes you, you, and not somebody else. If you had an identical twin, you are two different people. You, yourself, are not composed of concrete nouns (forgive me, I'm turning English major, here), but you are made up of abstract nouns. Things that can't be touched. Like loves, fears, hopes, regrets, beliefs, values, and so forth.
Normally you think of the opposite of love is hate, right? I did too. But at a writing workshop Steven James was speaking on characters. I learned that the opposite of love is fear. Interesting. But if you love freedom. You will fear entrapment, limits, and the like. This makes things a bit easy too. Because if you know what your character loves or desires than you already know what he fears. Or if you know what he fears, than he loves the opposite.
Maybe this is just me speculating on the spot, but perhaps fear is stronger than hate. If I hate spiders, I'd have an obsessive vendetta against spiders, smash every one I saw, go hunting for them. But if I have a deep phobia of spiders, I would cower and cry every time someone mentions the word 'spider,' and, if I was to see one- complete panic attack. Not saying that hate is good. Never. Hate is more like the enemy of life. It's the cause of death. But while fear holds you back from attaining your goals and keeps you from what you love or desire, hate is the passion the burns action toward your goals. If I hate spiders, I desire a spider-free world., and I will do something about it If I simply dislike spiders, I will probably desire that the place where I presently stand to be spider-free, I will again probably do something if need be. But if I fear spiders and although I desire a spider-free world, that fear paralyzes me, and nothing comes of my desires.
So fear is an obstacle that the character must overcome. Inner journey stuff. Make your character suffer stuff. Although the spider thing was kind of a bad pull-out-of-the-air example. The things your character will desire and love are more serious topics like freedom, justice, strong family relationships, mercy, and so forth.
Goals go along with a character's love or desires in a way. If the protagonist desires or loves freedom, one of his goals (stated or understood) may be to break free of something that holds him in bondage or maybe he has a friend or even a group of friends, a whole country held captive (figuratively or in reality, it's the wonder of books, nothing is impossible). A character may have long term goals or short term goals. And sometimes goals change or build on each other. "The Hunger Games" for instance, Katniss' main goal was to protect her sister. In doing that she realized that she not only had to take Prim's place in the Games, but she also had to keep her promise to do everything she could to win and return to Prim. And after she won, Katniss had no goals (until she found out she had to go back). She just survived. So a character doesn't always have to have a goal. Oddball, my protagonist, is rather goal-less in the beginning. In the Hunger Games many of the secondary characters had the long term goal of defying and destroying the government system of Panem. I'd say it was Katniss' too, but she was more dragged into it.
Values. This is more where the disliking will come in. If your character values life, he won't like death. If he's in a fantasy, he will be hesitant to kill his enemy, maybe wound him, but kill him? If your character values tradition, he won't like change. He will probably rebel at the sign of any kind of change. Or maybe he values new ideas and progress despite if it's a good change or not, than he won't like any kind of tradition. Back to "The Hunger Games," Katniss valued life. She even valued her enemies' lives- until they would threaten the the lives of the people she loved. She valued life. But she valued the life of the people she cared for more than the life of her enemies. Values can have limits.
A character may also have a sense of right and wrong. In life, one person may do something he believes is right, and another person may found it wrong. Some people may have a standard or moral code they follow. Like I believe the Bible is the standard for right and wrong. Other people think their own opinion or their own situation determines what's right and wrong. It goes partly with what characters value perhaps. Like Katniss would think that killing is wrong, even killing your enemy unless the life of someone you love is at stake. Also though, just because someone believes something is wrong doesn't mean that he won't ever do it. So a character may do something against what he believes. He may change what he believes in order to compensate for the inconsistency in his actions (psychology wasn't a complete waste of time, just almost). Or he may just feel guilty about it.
Other things that can hold a character back besides fear: guilt and failure. This goes a little more with backstory. But also with values, beliefs, and goals. If a character did something he believed was wrong or maybe he failed to meet a goal, he might hide it. He might care the regret with him everywhere. It's a good obstacle to throw in to make our characters miserable.
These are some rather vague examples, but the core elements of characters will help dictate how they will act, think, talk, etc. Along with their background (more on that later). So if the protagonist is in a situation and you're not sure how he would react just think back to his fears, desires, values, and so forth.