Never get high on your own product.
Ever since Labour’s sensational and better than expected general election of last year I’ve felt Corbyn’s been a bit hubristic. First there was him telling Michael Eavis that he would be PM by Christmas 2017 and now there’s JezFest that could cost see Labour with a million pound loss.
Despite the result last June Corbyn finished with fewer votes and seats than the Tories and it should be remembered that many observers said it was the worst Tory campaign in history.
Hubris leads to bad political decisions such as in the targeting of seats, assuming some seats are in the bag when they aren’t and targeting seats that were never in play.
Two examples I can think of is following their surprise victory in the 1999 European elections the Tory party assumed they had 100 gains in the bag for the 2001 general election and that turned out to be a very dangerous assumption.
The other one is Labour in 2015 thinking everyone who voted Labour in 2010 were in the bag, whilst the events in Scotland rendered that extremely flawed, without the eight Tory gains from Labour in England and Wales David Cameron wouldn’t have a won a majority.