It's my book, and the people in it have to do as I say, right? Well, not necessarily. Sometimes they simply refuse to act the way you want them to. And of course, it's your own fault.
You create characters, but every one of them is a conglomerate of "real people" traits. Therefore, they take on a sort of reality and have to act within the personality that you ascribed to them. They have to have pre-existing reasons to act the way they do, and as the author, you have to provide the reader with those reasons.
My biggest complaint is the law officer who takes an immediate dislike to the hero, sometimes just being snotty to him but in other cases locking him up, harassing him, or even beating him and dumping him oustide the city limits. I am only willing to believe that sort of thing if you give me some background on this nasty cop or if you build up to it with an adversarial relationship between the two. A stereotypical goon who likes to push people around doesn't cut it.
Often readers (and moviegoers) complain about the protagonist who does unbelievable things like meeting the killer in a secluded spot with no backup (often labeled TDTL: too dumb to live). Again, it can be done (has to be at times to make things exciting) with proper build-up, either a strained situation or a risk-taking personality.
Then there's the character with the smart mouth. Authors like to write snappy dialogue, but again, the situation and the personality have to be perfect or they're just showing off. Unless the character is well-drawn as one who's compelled to make flippant remarks, he just comes off as irritating. I might want to beat him and drop him at the city limits myself.
We have to have tension to make stories work, and tension comes from people's inner motivations and outer manifestations. Scarlett O'Hara irritates the heck out of you as a reader, but you never doubt that she would do the things she does. Her personality demands that she pursue her own interests and ignore the needs of others, and Mitchell shows the reader from page one what Scarlett is like. After that, we not only agree that she would chase her best (only) friend's husband, we expect it. If you know your characters thoroughly and present them as "real people," they will act in ways that are true to their needs, and readers will never ask, "Why did she do that?"