It's not something they readily admit to you in social studies class, but it will almost never make any difference whether you, personally, decide to vote or not. In our winner-take-all system, the margin of victory doesn't matter, only victory, and rarely does victory hinge on a single vote. Rarely, but not never. Take, for example, a Republican congressional primary in Michigan yesterday.
According to the Michigan secretary of State, with 54,181 votes cast between them, tea party candidate Dr. Dan Benishek leads state senator Jason Allen by a single vote, 27,091 to 27,090. The AP's count is slightly different it has Benishek up by twelve votes and there will definitely be a recount, which is bound to change the results in unpredictable ways. But the amazingly close race serves as a reminder that sometimes, in very rare circumstances, performing your civic duties may be worthwhile if you hadn't already learned that lesson from The Simpsons.