In the following spoiler, I'm posting a link to a video of a street fight. If you don't want to watch someone getting knocked out, don't click the link, please. Spoiler Notice the guy in the black shirt that's trying to talk the hothead down. He gets slapped in the face and is extremely put off by it, but is content to just stand there complaining about it. The second the aggressive dude goes down, the previously nice guy flies into a rage and tries to kick him. It's a really fast change in heart. In fiction, most characters most of the time are hyper consistent. If someone likes pizza once, they will want pizza every time it's offered. If someone doesn't back down from a fight, they will never back down from a fight. The behavior of real people is much less consistent than fictional people. So if you wanted to have a character have a rapid change in heart or behavior, how would you make it convincing. Imagine that the victim of the slap in the video isn't the POV character., and you can't monologue about his internal thoughts.
I'm not seeing Black Shirt the same way. It looks to me as if he is trying to protect Red Shirt, and Red Shirt is trying to get him out of the action. Instants before Black Shirt gets slapped, he's trying to block the guy's path to Red Shirt. The guy hits him and gets past him, hits Red Shirt, and then gets hit by Gray Shirt as Black Shirt is recovering. But as I see it, Black Shirt wants revenge for the guy hitting Red Shirt. I realize that this doesn't actually respond to your question, though it may be relevant--the issue may be about a non-obvious motivation. Black Shirt's behavior is inconsistent if you only consider him as an individual, but when Black Shirt and Red Shirt are seen as a pair, with Black Shirt's primary motivation being to protect Red Shirt (followed by anger when that goal fails), and Red Shirt's primary motivation being to keep Black Shirt from getting into the fight, I see their behavior as consistent.
Good points. I'll have to watch it again. It didn't look to me like red and black were in a group together. Edit -- I see it now. I missed the first bit when black shirt was up front. I thought he was just standing in the crowd.
Video aside, you have to think about what's going on in someone's head. People may not appear consistent because we're not aware of everything that's going on and influencing them -- and we reach breaking points. A character who's normally very emotionally stable and strong can have too much put on them and snap, or be affected by something that seems minor but has personal significance to them which makes it much heavier. An outsider who doesn't know that person very well won't be able to see all the factors in play. So if you want a sudden change in behavior, you want to push that character to their breaking point. Like I said, it can be a lot of stuff, or it can be one specific thing -- think Marty McFly, a usually pretty easy-going dude, when he gets called chicken
Everybody's got a breaking point. I do, you do, your mom does, your grandma does. What we do after that might be different, but everybody has that point. It's a combination of past experiences, who you want to be (who you believe you are), and who you actually are. Some people are protectors. Black shirt might be one of them. Most people have that 'one insult' they just won't take. For Marty, it might have been being called chicken. Some might not respond well to having their mother/sister/wife insulted; others, the size of their manhood; others still, an insult about physical ability. To muddy it further, just because a certain person could trip that breaker switch, doesn't mean everyone could. There are probably jokes your friends could make about you/to you, that you wouldn't take from a stranger or someone you hate. There's a very fuzzy video of Orlando Bloom and Justin Bieber in a nightclub. As long as Bieber is insulting Bloom, he laughs it off. But the moment Bieber takes a verbal swing at Bloom's wife, Bloom takes a physical swing at Bieber. A lot of people are like that; the mindset of "Do to me, I don't care. Do to those I love, and you'll regret it." I'm honestly not certain what goes on in the video you posted, so I can't really speak to it, but if you want to have a character turn violent, understand what makes them tick. It's not entirely unreasonable to assume that *most people* (not all, certainly, but most) will fight when backed into an emotional corner. Even I've had violent urges when the wrong person has insulted me, and that's not something I normally do. Some people crack under pressure. Some explode.
Erm, being inconsistent is considered a bit of a problem in the medical circles . Which doesn't mean impulsive behaviour isn't a thing. But it's a different thing. You just have to keep in mind all those different things that make people do stuff. And, unless you got a Mary Sue, a fiction character would also be shown to do something "inconsistent" at the right moment, so that a point can be made.
I am not a member of these "medical circles" so please take my thoughts with a grain of salt )), but I thought that personality tests a la Myers-Briggs took inconsistency into account. Why else do they ask essentially the same questions over and over with slightly different wording? I understood that it was to see to what extent your opinions were consistent and under what circumstances they varied. Anyway, to answer the original question, I would imagine that a believable split-second change of heart would depend very much on the preparation put into into. As other posters have said, we need to understand the character's motivations and deep values in order to believe a switch.
What I mean by inconsistent is how the behavior of people vs. characters appears. Of course, I'm not saying real people act spontaneously without cause. But the causes can be subtle. For example, a person inclined towards stealing may or may not steal from his friends / parents / patients every time. He might only do it on days when he didn't sleep well or feels a little hung over / in a bad mood. On days he feels good, he might rather leave their stuff alone. Contrast that with a literary character, who will either always steal when he has a chance, or never will even when tempted. If he does steal once, it will be set up with huge amounts of exposition or be a big deal. Most of the time.
I'm starting to feel like a warped record here, skipping back to the same groove over and over—but this is where internal thoughts and feelings come in. Writers hamstring themselves trying to tell all stories just using a combination of dialogue and action. And you've shone a spotlight on why. Actions and dialogue often don't reveal what's going on inside a person's head. Movie scriptwriters and playwrights write dialogue and stage directions. They expect that the actors, through body language, facial expressions and tone of voice as well as actions will communicate more emotion and thought process to the audience than the words alone reveal. As a short story writer or novelist, you have command of all of these things PLUS direct access to actual internal thoughts and feelings. If your POV character suddenly does something 'out of character', YOU have access to why they've suddenly changed their minds or exploded or lost their temper or decided to change tack or whatever. You're inside the POV character's head at all times, so you can reveal to the readers what is going on 'in there.' On the other hand, if some other character is suddenly doing weird stuff, you can get your POV character to wonder about it, or speculate why, or be confused as to why, etc. Your POV character might think something along the lines of: I thought he was such a mild-mannered little fellow, and he suddenly whacks off the head of his sister's doll? What provoked THAT, I wonder? Maybe he's more upset about the divorce than I realised....
