Taking responsibility for the things you do is a learned skill -- one that doesn't come naturally to preschoolers. "They don't yet get the link between their actions and the consequences, so when something bad happens, they don't know what's to blame," says Karalee Bechtol, a licensed marriage and family therapist in Pasadena, CA. "It's easier to have something to project their anger onto."
Scapegoating inanimate objects is one thing, but if your child regularly points the finger at innocent pals (say, whining that his friend bumped him and made him drop his ice cream cone, when he really just lost his grip on it), it could lead to problems later.
A recent Canadian study found that children who take their wrath out on peers early on are more likely to be bullied when they're older, perhaps because kids see they're easy to get a rise out of.
So don't let misplaced blame slide. Be sympathetic to what's happened, but talk it through rationally. Say, "I'm sorry you fell, but your sneakers didn't do it. That's silly!" It may take a couple of years, but eventually your child will comprehend that his behavior has consequences. Getting him to admit it, though -- well, that's a whole new challenge that awaits.