To put it bluntly, casting your ballot solely to effect the outcome of the election is irrational. Let me put it in an equation: (benefit per person from your candidate) x (300 million people) - (personal cost of voting) = Expected Utility of Voting
I'm believe that this equation equals a negative number for most, even if you're in a swing state. So you may ask, why did Harrison vote today?
1) To both make myself feel good and to support those who think like me.
2) My Republican votes for the United States Congress were votes for a divided government.
3) My Libertarian votes for President, Governor, as well as other minor positions were to call attention to my team. Every incremental vote gives the two major parties the incentive to move that way.
4) My reasons to not vote would have been at least partially motivated by my self-deceptive thoughts on my political superiority,
5) It gives me political season closure.