Ever reached the frustration point and said something mean, then wished you could take it back?
Ever misjudged speed and cut someone off?
Ever had a thought pop into your brain, and you say it--then realize how STUPID that was to say? How it might even have really bad consequences, just because you let it out into the air?
Ever get impatient with somebody taking forever, then find out there was a damn good reason for it?
I have. That one happens too often.
Everyone makes mistakes. Everyone (as far as I can tell) loses their temper, says stupid things, DOES stupid things, gets wrapped up in their own world and loses sight of how their words, their actions, affect people around them.
What I find interesting is when people get trapped in those mistakes.
We just saw a GREAT movie, an adaptation of W. Somerset Maugham's book The Painted Veil. I won't reveal spoilers, but a major focus of the plot is one character's refusal to allow the other to make up for a mistake. It's like he boxes her in that moment--where she'd erred--and will never let her get past it.
Something similar happens in Rachel Getting Married. Kym (played by Anne Hathaway) made a horrible mistake, yes. Horrible. And in a series of mistakes. But to the people it affected, she can never get past that point, that one decision failure--because of the consequences. And the movie is (partly) about both she and her family TRYING to get past that point.
I find this fascinating in writing too, of course. Characters are always going to make mistakes, little mistakes of temper or lack of awareness. And isn't it intriguing to follow the consequences of those mistakes? To explore what happens when something awful happens because of your character's mistake--or the relief when she realizes something awful MIGHT have happened, but didn't. That time.
Mistakes make us grow, hopefully. They also reveal us as real, as frail. They reveal your characters in ways that will make them real to readers--and readers will more easily identify with people like them. People with tempers and impatience and stupid-mouth. I think it's important to be aware of that dimension in your books, to play with it. Follow the mistakes, and see what happens.