No government election has ever been determined by a single vote, outside of a couple small town positions. Your vote doesn't matter and that's why you get to do it.

To extend the logic a bit; even if an election were to come down to a single vote and you do decide the outcome, your vote is still only worth the difference between the two leading candidates. Since those are usually both awful choices, that's not a lot of value.

Additionally, if it's a vote for a member of a voting body (like Congress or Parliament), your vote would still only have mattered in cases where those representatives were tied on an issue, which doesn't usually happen.

Maybe someone can prove me wrong, but I think it's fair to say that not one person's vote has ever made a difference.