I am told Jean-Claude Juncker learned just one thing from Boris Johnson on Monday in Luxembourg.
In the words of one of his colleagues there was "confirmation that the UK (under Johnson) wants more of a border on the island of Ireland than the previous government".
Which is the nutshell of the whole of what the PM seeks qua new deal and what the EU’s 27 leaders need to evaluate either as deft compromise or as brutal betrayal of Dublin and the Good Friday Agreement.
This dispute harks back to the December 2017 joint agreement between the UK and EU which pledges to prevent the creation of "a hard border including any physical infrastructure or related checks and controls".
This matters because Theresa May’s Brexit - the Withdrawal Agreement - says "any future arrangements [for Ireland] must be compatible with these overarching requirements".
And that would render illegal pretty much any method of keeping open the border between Northern Ireland and the Republic of Ireland, other than membership of the customs union for Northern Ireland or the whole UK, combined with significant regulatory alignment with the EU for NI or the whole UK.
For Johnson and his top aide Dominic Cummings, unless the EU 27 allows some new infrastructure and associated checks and controls somewhere in NI, there would be no escape from what they see as the serfdom of either NI or the whole UK being bossed to some extent by Brussels, perhaps forever.
And although when push comes to the shove of an imminent no-deal Brexit, Johnson may be less anxious than May was about putting a regulatory border in the Irish Sea.
At this juncture he desperately needs to assess whether the EU can be just a bit more flexible about the use of supposedly unobtrusive technology to keep rogue goods and food out of the EU single market.
I doubt the EU will budge, but Johnson has to ask.
Robert Peston is ITV’s Political Editor. This article originally appeared on his ITV News blog