I've noted before that politicians begin their slide into ignominious defeat when they start believing their own propaganda
Quite what planet Theresa May is living on, heaven only knows. All of three main Brexit parties suffered loses (Conservatives, Labour and UKIP) the two Remain parties (Libs and Greens) made gains. Only Theresa May could interpret this as evidence that the people want to leave. Even Corbyn, who must be guilty of one of the worst political miscalculations in history, seemed to concede that he'd lost votes because Labour's remain supporters had gone to the Liberals.
Corbyn probably has an understanding of the Labour movement, he has much more exposure to it, but I'm far from convinced he has any grasp of the mood in the Labour voting coalition. For the most part the latter aren't political active, but they're the sorts of voters that Labour needs every five years, and they're nothing like as dogmatic as the activists who Corbyn tends to see more of and hear more from. He's made the fatal error of mistaken the loudest noise for the mood of his vote. The time was Christmas 2017 or Jan/ Feb 2018 to alter course and have it confirmed at the party conference in the autumn. If he'd done that, he'd be about 15pts clear now
The real tragedy for Labour is that this was so foreseeable. You honestly didn't need to be a political guru to spot this opportunity. It had flashing red lights and a siren on it. The daft thing of course is that Corbyn still seems to think he's the solution and the only thing that can save the country is him being PM. He hasn't worked out that he could only form a coalition government dependent on SNP and Liberal support, and they'd make revoking A50 conditional. It's really, really bad politics on Corbyn's part