The EU will not want to do anything that harms their economy,
The EU stands to lose out post-Brexit, in terms of global export revenues, but the UK faces three, four or five times the losses - in percentage terms - in automotive, consumer, healthcare and technology and that's just a simple financial fact. Baker McKenzie did a detailed study and summed it up very succintly. The bottom line is that as Boris walks into those talks, "the EU exports a lot more broadly, to a whole host of other markets, and consequently, it is far less dependent on the UK as a market than the UK is on it."
He now has power over The EU.
He has no more power over the EU than he did when he agreed to the revised withdrawal agreement and compromised dramatically on all the things he said he wouldn't. Johnson entered the negotiations insisting that a customs border on the island of Ireland was an unavoidable side-effect of Brexit. He offered only selective alignment for Northern Ireland on EU agrifood regulations and his famous 'alternative arrangements'. By the time the deal was struck, he had accepted not just a regulatory and agrifood border down the Irish Sea but a customs one as well within the UK.
Some will be a problem, like fisheries.
What do you think is the main problem - any suggestions for Boris as to how to solve it?