In a well-functioning democracy you'd vote on someone who you'd agree with on something like 9/10 issues. However, not everyone agrees with you, so they might e

In a well-functioning democracy you'd vote on someone who you'd agree with on something like 9/10 issues. However, not everyone agrees with you, so they might end up having to create a coalition with someone you agree with on 6/10 issues. In the end you end up with 7.5/10 issues going your way. Not ideal, but not too bad either. In a first-past-the-post system, voting on the 9/10 politician is a complete waste as everyone knows they'll never get a majority. Plenty of people like the 0/10 guy, and the 3/10 guy is quite popular too. So better vote for the 3/10 guy: sure, you don't want him, but having him in office is still better than the 0/10 one winning!