Check out our discussion of "Fate and Free Will" for some thoughts about whether or not the choices of the characters in Holes even matter. Whether or not they matter, though, they're definitely made. Whom to marry, how to act, what to believe – most of our characters do some pretty decisive choice-making. Oh, except for our protagonist, Stanley: for most of the book, he's pretty content to let other people – more powerful people – make choices for him, while he just follows along and makes the best of things. He usually reacts to conflict passively, trying not to make waves or assert himself too much. Is Stanley's choice not to make choices a worthwhile one for him?
Holes is about Stanley learning to make choices for himself and not just letting other people – or circumstances – make those choices for him.
Stanley has no trouble making choices, it's just that his choices are limited by his situation; he doesn't have a lot to choose from.