There are many things that can irk a reader out of your story, and having your characters act out of character is one of them. Probably one of the biggest in my opinion.
We writers sometimes fall into the trap of forcing something to happen to push our story along. Rather than work on the plot and maybe rewrite a few chapters, we decide to push our character into a situation where they don’t belong. This, friends, is a big no-no.
For instance, if your character is very against alcohol, and the first time they meet a cute guy/girl who wants to go to the bar, they should NOT go. Nobody gives up heavy convictions that quickly for strangers, no matter the attraction.
I realize that’s kind of a random example, but it illustrates my point clearly. Be careful what you have your characters say and do, because readers can spot the lies a mile away.
So how do you avoid this mess? Get to know your characters. It’s that simple. What would they compromise for? Why? Make sure your reader is aware of this, even if it’s only through subtle hints.
If you’re simply forcing your character into a situation because you have no choice, change the situation or change the character. It’s not easy and definitely requires a lot of work, but that’s writing for you, and not to be too sassy, but you (and I) chose this life.
There are so many ways to get to know your characters, but I would suggest a good ol’-fashioned character sheet. This site has tons of great questions you can work on to really dig into your characters emotions/intellectual abilities/physical traits: http://birdsofawriter.blogspot.com/2011/07/writing-tips-character-sheets.html
I suggest you answer most, if not all, of the questions they pose for your main characters. Maybe even write a little backstory for them of a big moment in their life. It’s tedious work, but your manuscript will benefit from it, which is something you and the reader both want.
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