This doesn’t make much sense at first sight but the mind works in mysterious ways. People know there are others who think the same way they do and if people like them don’t vote then their candidate is unlikely to win. Therefore they need to vote themselves.
It sounds like a twisted kind of logic but Quattrone & Tversky found some evidence for it in a study following on from the one they did about self-deception (see the connection?!). They found that in a simulated voting situation participants behaved as though they believed that their own vote actually caused other people to vote in the same way they did.
In other words, people seem to behave as though their own behaviour is diagnostic of other people who think the same way.
This is another neat demonstration of our powers of self-deception and one reason self-deception can work to society’s advantage. Democracies generally view voting as a good thing (with some notable exceptions!) and try to encourage it, yet people rationally understand that their individual vote makes practically no difference. But when we see our vote as signalling how others will behave, it becomes much more important.
via Why Do People Bother Voting? | PsyBlog.