Motivation

I am reading a book where the author doesn't take full advantage of showing what's going on in the main character's head and so some of his actions seem abrupt and out-of-character. Here's an example of what I'm talking about:

Sarah stomped up to Rebekah, who was smiling and holding another book clutched against her chest. Sarah scowled and threw the current book Rebekah had loaned her to the ground. "This book was horrible. I swear, I'll never read another book by that author. In fact, you couldn't pay me enough to read another one!"

Rebekah said hesitantly, "Oh, I'm sorry. I brought the next book in the series with me, but I guess you don't want it."

Sarah felt a surge of anger. "Of course I want it. The book's right here, so of course I'll read it."

You're left wondering why Sarah suddenly changed her mind and why she's reacting so strongly. Or, if you're like me, you're feeling a little wary of Sarah and wondering if she's insane. ;)

I expect the author knows a perfectly sensible reason why her main character acted the way she did but forgot to let the readers into his head so we also know. Here's an example of how adding motivation can help make an about-face scene like this make sense:

Sarah stomped up to Rebekah, who was smiling and holding another book clutched against her chest. Sarah scowled. She'd rather liked the book Rebekah had just loaned her, but she didn't like how her friend was getting into the habit of forcing books on her and she wasn't going to allow it to happen again.

She threw her book to the ground. "This book was horrible. I swear, I'll never read another book by that author. In fact, you couldn't pay me enough to read another one!"

Rebekah said hesitantly, "Oh, I'm sorry. I brought the next book in the series with me, but I guess you don't want it."

Sarah felt a surge of anger at Rebekah for picking this moment to finally bring a book she did want to read. "Of course I want it. The book's right here, so of course I'll read it."

Sarah's still not a very nice character, but at least we understand why she's acting the way she is. So, authors, be careful not to throw an unexpected emotional reaction at the reader. Make sure to get into the character's head and explain why they felt that way so the emotional reaction makes sense.