I think something has to be said about people in the game who attempt to portray 'characters' of their imagination as part of the 'role playing' motif. That is, the desire to produce a character distinct in its portrayal from the player, so that the player's fighter, say, does not do what the player does, or believe things the player believes, or otherwise views the world as the player might view it.
For example, the player, being a typical resident of the 21st century, is unlikely to scream bloody murder, raise the axe in their hands, and attack a seven-foot-tall monster ... where as their fighter would. More to the point, however, the player would probably try to survive in a given situation as best they could, whereas their fighter might not.
Those are perfectly reasonable character portrayals.
Unfortunately, when a player usually decides to produce a really elaborate character ... well, they just suck at it.
For those who can't quite grasp the substance of what 'character' means, I offer this lengthy definition. Please take note of the bottom of the definition, where it describes two states: "in character ... Consistent with someone's general character or behavior"; and "out of character ... Inconsistent with someone's general character or behavior."
What's required, then, of a writer, or a presenter, is the creation of characters for whom "in" or "out of" character has a specific, defined and recognizeable pattern. This is obtained by providing characters with motivation, a PURPOSE or LOGIC for why they behave the way that they do, so that the character as portrayed isn't a bunch of irreconciliable actions that fuck up a performance.
Writers almost always draw upon their own motivations because as human beings (questionable, but there you are), they are unlucky enough to be limited to their own experience. At best, I can only guess why the fellow further down the bar is right now stupidly drunk, or why he obviously has a lot of money to spend on drink after drink, or how he's able to stay on the stool even though he's been doing this now for 7 hours. I can only guess at why the bartender goes on serving him. I can only guess these things because I am not them. If I were to pretend to be them, I still wouldn't understand their motives because it took a long, long time for those people to become who they are ... whereas I've spent all my time becoming who I am.
So as a writer, I am always at my best when the various characters in my work represent different sides of myself, and not wholly disparate people with whom I have no association. At best, I might attempt to include the characters of people I have known all my life, such as my mother or father, or friends I have known since childhood, or co-workers with whom I have spent thousands of hours. I know something about these people because they have explained or demonstrated their motivations. I grasp them.
Moreover, I have practiced this technique. And when I say that, keep in mind that all the writers who have written all the really crappy TV Shows and Movies you have seen have also practiced this technique, and the best they've been able to produce are very ordinary, instantly recognizeable stock characters whose motivations are poorly drafted and often compromised by some situation where the writer has plainly gotten himself or herself stuck. Remember that everyone who talks about film and television spends many more thousands of hours talking about how such-and-such was not in character because "blank-blank-blank would never, ever do that."
Character portrayal is HARD. It has always been HARD. It is difficult to describe honestly your own motivations; describing another person's motivations is IMPOSSIBLE. But we try anyway, in the hope of getting into the ballpark, because other people are so gawddamn fascinating. Or rather, other people's stupidity is so gawddamn fascinating.
Here is how NOT to produce 'character': Have it do something you wouldn't do, because you wouldn't do it.
I don't know how many times I've run a game where some player got it into their head that their 'character' would be insulted about something which most obviously the player is not. The player gets the whole situation. They're genre-savvy, or they've been paying attention to the nuances, or they don't care that much about the priest, the princess, the king or the warlord. So when the warlord gives an order, the PLAYER is all like, "Sure, I get that, he's a warlord, he's got to keep himself in control."
But somehow, the player decides to interpret this from the character's perspective as, "What a fucking dick that warlord is, I'm not taking any of his shit!"
Which baffles me. Presumably, if the character were a character in this medieval world, the character would be just as clear about a warlord - having now met one - as the player would be. One might assume the character would have a better grasp on the situation, no? And be a bit more conscious of actually being in the warlord's presence, and seeing the warlord's army standing right there, looking all frightening and ready to go. But nooooo ... no, the 'character' presented doesn't care about any of that. The character's motivation in this instance isn't affected by any will to survive, or any recognition of having grown up in an environment where warlords have absolute power. Nope. This character has been beamed in from outer space - or possible from bad 1970s television - and remains untouched by the environment that surrounds them. This character turns to the warlords and says, "I demand attention and I demand that all my demands be immediately satisfied because I have just made demands!"
Somehow, every concocted Dungeons and Dragons character seems to be motivated to make demands on a constant, continuous basis, like an old woman at the complaints counter of the local Walmart, who can't understand why her panties can't be returned after having been worn for three weeks.
The problem, I think, is an inability to put oneself in the situation, and see the situation with the eyes of a person who is actually there. As a DM, I can describe the appearance of things; I can describe the sights and smells, the noise, the apparent activity of the natives ... but I can't make the player graft those things into the player's brain. If the player chooses to hear the words, "the children run through the streets banging pots," as WORDS, and makes no effort to pause for a moment and contemplate what that must sound like, or what that must look like, then I cannot as a DM force those images into the player's head. The player is then free to invent 'characters' utterly divorced from their surroundings, who are even less motivated or affected by those surroundings than the player. The player, at least, is aware of what THEY would feel like if transported into a fantasy world and forced to cope. The player, however, has no fucking clue at all what an imaginary, non-existent character would feel, because they don't know that character. They can't.
So the whole exercise is a dead loss. And over and over - as someone who DOES try very hard to imagine how I, or someone I know well, would act in a fantasy world, or how a warlord would deal with someone of no importance who made constant demands - I am forced to kill characters in stupid ways for stupid reasons because they are stubbornly portrayed by stubborn players.
It has much to do, I think, with a lack of humility. Players don't understand the difficulty of creating a character. They don't suppose it is difficult. They suppose it is a matter of 'talking differently.' Cognitively, it's not only that they don't get over the hurdle, they don't see a hurdle. And when they stumble and fall, they get up gobsmacked and angry, presuming that they must have fallen because someone pushed them. It's simply not possible that they were tangled up in their own bloody hubris.