Press reporting of Polls
I saw no mention of how accurately (complete with caveats) the poll results were reported! I'm sure that has had a significant effect on the four recent unexpected results (General Election, EU Referendum, US Presidency and the vote in Italy this weekend).
Voters don't seem to like to be told how to vote!
I can't see any politician around the world calling an election unless they absolutely have to or have fixed the result in advance (Russia?)