Paul talked about having a thorn in his side, that he struggled with, and although he prayed, he still struggled with it.

I think it's normal for a person so have one particular sin that they struggle with more than others. Whether it's anger management, lust, pride or etc.

What sin does your MC struggle with, and how does it affect him and his character?

Hm, this is a good question.

In a suspense story I have in the plotting stages, the MCs all have various problems they are coping with. (More so than most of the characters in my children's stories) Collin is a recovering addict and alcoholic, which brings up a lot of interesting points with the characters. But with him, it's a major point in the plot.

My character Paddy was disrespectful and disobedient to his father growing up--eventually chasing his parent away--but for good reason, because his father was not a nice man and was a threat to the family. Paddy likes to break the rules, but for good causes. This background with his father, though, affects him in the respect that he just really, really wants to be a husband and dad--and to be the best one in the world, in spite of his father's example and to sort of "redeem" from what his family had to put up with.

I have another character who is vaguely alcoholic, but he doesn't see a problem with it, which is interesting to deal with, too. I've not written enough of this story to know how it ultimately affects him and those around them yet. A character in that same story deals with abandonment and is always ready to run off on people; he also holds grudges.

A lot of my characters seem to be chronic liars. Not really sure what that says about me...

One of my main characters does struggle to be nice to his annoying sister, but I don't think that's exactly what the thread meant. Another main character struggles with hatred towards his masters (he's a slave). Yet another struggles with self pity because her circumstances made the life she wanted impossible. (And yes, these are all from the same story. I have a lot of characters.)

I think that limiting to just a sin tends to provide too narrow a focus. There are lots of things that can serve as a thorn without being a specific sin. Attitude can be one. Habits. Health issues.

Hope deals with a lot of different things that could be a thorn. She's in a cycle of abusive relationships, abuses painkillers, has low self-esteem, and seems to suffer from schizophrenia. Plenty of thorns there.

Hmm...

Leo from "Catherine's Miscreants" (1960's spy) struggles with being emotionally real. He's like James Bond when on a mission yet he goes back to suburban Trenton and tries to figure out how to ask his helpful neighbor out on a date. He's bought her teen son a Burpees catalog and they had a rousing time when he bought a Frisbee. Life's a lot harder when you can't just shoot people.

Billy, also from "Catherine's Miscreants" just had his wife leave him, hit bottle hit empty, and his step-dad's arch enemy's daughter ask for help.

Marco from "Domici Wars" (Sci-fi military) has way too many beautiful women around while he tries to remain emotionally and physically loyal to his girlfriend. They have been intimate once, and unknown to him he's about to be a dad. Yet he's on another planet leading a rebellion and she's in jail for a murder she didn't commit. That she's a head taller than him and twice as strong does play a part, but he's a Christian and trying to be true to his faith, even though they messed up once.

Ang, also from "Domici Wars" is an emotionally distant cop who just found out her supposed ex never actually filed the paperwork. She hasnt' shot him for running off with that Navy pilot. Yet.

Tala, also from "Domici Wars" is an ex-exotic dancer Psion who continues to love the man who rescued her and tries to teach young mental adepts to like themselves, even though she still struggles with it.

I agree with Varon that "real people" often struggle with multiple issues at once and will make mistakes all over the map. However, in the context of storytelling, we are usually focusing on one aspect of our character, whatever relates to the theme/message of the book or is most central to the plot and the character's development. So in the planning/plotting stages it may be best to focus on the issue you want to drive home, but when you write the actual book, it wouldn't hurt to have your character mess up in other ways for realism.

It's also worth noting that while "real people" almost always have multiple sins/weaknesses that need to be dealt with, God is gracious and usually just tries to get us to correct one at a time. There is usually an issue that He drives to the forefront of our minds because it's a priority for Him--or your current life circumstances make it a priority.

What's interesting is, if you study the character faults and growth portrayed in many movies and books, you'll find that all the characters are struggling with a different facet of the same issue.

Can you tell that God may have been working with me on a few things lately?