Just recently I was reading a book a friend lent me and told me I just had to read. What was funny was how he told me the first 3 books were great, but the ones after weren't worth it. Didn't sound like something I would want to get into, yet since he went to the trouble to bring me one of them, I thought "why not?".
Within the first few pages I hit something that just about made me think there was no point in reading it, regardless of the good prose and likeable characters -- clash of character vs writer's plot direction. In this particular book, a man who lives in a non-magic land and is very well acquainted with nature, comes across a plant. He cuts the plant, and it hits him with a thorn. When he tries to remove the thorn, the thorn embeds itself deeper into his hand. He has no knife, so does what he can, but the darn thorn acts unnaturally and evades his attempts by totally disappearing into his flesh. He mucks with it for another moment, and then for all intents and purposes, shrugs his shoulder since he can't do anything about it and goes on. Now, hold the phone! Anyone in their right mind who had a thorn dig itself into their hand and saw it do it would be screaming bloody murder and trying to get themselves to the nearest doctor. (I would!) Yet this man forgets all about it, except for noticing occasionally how the hand turns red and hurts (like that shouldn't be sending panic signals), and goes on his way getting into the meat of the adventure.
In my opinion, there was a definite clash in what the writer wanted to set up as a later problem, and the believability of what the character did about it. Personally, I would have fallen for this if the guy panicked a little, did try to go home to get help, and on the way got distracted at least for a short while, by other events going on around him. So this clash could have been averted or minimized, but the author was too intent on his plot and not his people.
As a writer, a lot of times you will try to stick to a mental road map of where the story needs to go. But you have to absolutely stay true to the motivations and characteristics of the characters you are portraying or you will be doing the whole novel/story and your readers a huge disservice. Listen to what the characters tell you, even if it's not part of the map! If you just have to have something happen in the story, but it clashes with your character's motivation/personality find a way to shift the situation so they will do what you want, or ditch it. Don't force it!
Here's an example: An old saying is that Tonto (The Lone Ranger's Sidekick) never goes into town. "Tonto no go to town." But in order for your plot to progress you need him in town because only in this way will he meet the beauty from Boston and fall in love. So what do you do? You can't just suddenly have Tonto say he wants to go to town. That's totally against his usual motivation/personality. (Town is a dangerous place for Indians. Ripe with trouble.) But if he absolutely needs to be in town, then arrange the consequences, which with his personality, will make him go to town. For Tonto, this is easy. If the Lone Ranger went to town and was not heard from in too long and he knew things were dangerous to begin with, he would go to town to look for his friend. If he received a message that the Lone Ranger was in trouble, this would also drive him to go to town--his need to be there for his friend overruling his bad feelings about going to town. And all of it still keeping him in character and you still getting to where you want to go.
Know your character's personalities and motivations, don't let the planned plot shut them out. The more believable and reasonable you can make the choices they make due to the factors you've thrown at them, the more fun the story will be.