One definition of an ideologue is a person who responds to the collision of opinion with reality by insisting that reality must yield.

There are times when stubbornness is admirable, when formidable obstacles must be overcome by transcendent principle. Without that idea, Mahatma Gandhi would have bowed to British colonial rule. Rosa Parks would have surrendered her seat to a white passenger on an Alabama bus.

But in those cases, systemic prejudice ruled out negotiated compromise. Brexit is not such a case, and David Davis is no Rosa Parks.

The Brexit secretary is certainly stubborn when it comes to belief in his own abilities. He is also on a collision course with a wall of reality in Brussels. It is a stark fact that Britain’s prosperity and security depend on his technique for navigating that obstacle.

Early signs are not encouraging. It would be silly to extrapolate too much from the photograph, published on Tuesday, depicting Davis empty handed at a table opposite Michel Barnier, his European commission counterpart, who is holding a heap of notes. Officials say the snap was taken before UK team members had unpacked their own stack of documents.

But, as is often the case with such episodes, the awkward optics reinforced a valid caricature: Davis as an amateur trying his (and his country’s) luck against professionals. It did not help that Davis was on his way back to Westminster within an hour of the picture being taken. The defence was that underlings remained and got down to business.

But it is another stark fact of Brexit dynamics that Barnier’s staff are drilled in EU process and law. They are playing at home. Team Davis has hardly laced its boots. Whitehall is unable to plan for the government’s desired outcome because no one knows what it is. The UK is also unpractised in negotiating in Brussels as an external party because we have, until now, been an integral component of this thing called Europe.

British “position papers” on technical aspects of the negotiation (how to trade in nuclear material when article 50 requires exit from Euratom, for example) make painful reading for anyone seeking reassurance that Davis’s department is match fit. They are vague summaries of problems without solutions, as if the authors are only now beginning to grasp the challenges, through the act of writing them down for the first time.

British officials could not build a workable Brexit model before article 50 was triggered because the prime minister would not divulge her preference. She then squandered weeks on an election campaign that turned ambiguity into paralysis.

Day two of Brexit talks – and the UK looks as underprepared as ever | Jennifer Rankin Read more

Anyone imagining that a strategic intelligence lurked behind the scenes should ponder Davis’s assertion last July that the UK could expect to conclude trade deals with the US, India, China and Japan among other countries, starting in September 2016. “Within two years, before the negotiation with the EU is likely to be complete ... we can negotiate a free trade area massively larger than the EU,” he said.

Where are those deals? As long as the UK is part of the single market and the customs union – which it will be until at least March 2019 – there can be no external trade pacts. Thereafter, an optimistic expectation for the duration for such complex talks is five years. Put politely, Davis was talking out of his article 50 ignorance.

That might be cited as evidence to support the charge levelled this week by Dominic Cummings, former head of Vote Leave, that Davis is “thick as mince, lazy as a toad and vain as Narcissus”. Yet the jibe, typically unkind, was also unfair on two points. Davis is neither stupid nor idle. Arrogance alone could not have raised him from a penurious childhood to the top of government. He is energetic and cunning. But his skills are suited to a peculiarly British mode of advancement: the celebration of swagger and bluff over due diligence. Davis has benefited from Westminster’s generosity to men who gamble and busk their way through scrapes born of their own ill preparation – overgrown schoolboys who shirk their homework, then talk their way out of detention.

It is a trait Davis shares with Boris Johnson, one of his rivals in a succession battle, should Theresa May be deposed. Both have a reputation in government for ignoring their briefing notes.

Viewed from Brussels, where there is a higher premium on command of boring detail, it is depressing to see the question of Britain’s European future yet again subsumed into a parochial Tory pissing contest. It is irritating too to Brexit realists in the cabinet, one of whom has urged May to slap down the testosterone-fuelled “donkeys” in government.

Davis’s allies say completion of Brexit is his only goal, after which he intends to retire. That denial does not rule out finishing the job from No 10, should a vacancy arise. Supporters also say Davis is also pragmatist – unlike the wilder ideologues, who prefer a frenzied bolt out of the EU exit to a staged departure.

Davis has yielded to some realities. His early bravado has been tempered by recognition that aspects of the job “make the Nasa moonshot look simple”. He accepts the need for an “implementation phase” to Brexit. He knows that some payment will be made to settle the UK’s EU budget obligations. He has forged an alliance with Philip Hammond, the cabinet’s leading advocate of the view that drastic rupture from the single market would be ruinous. But awareness of potential calamity is not proof of a strategy to avoid it. Assurances of Davis’s sober intent cannot expunge his record of maverick gestures.

The Apollo 11 mission is a better metaphor than the Brexit secretary realised. It took the best part of a decade to plan. It cost billions. It was delivered by forensic expertise, not cocksure improvisation. Besides, getting to the moon was only half of the job: Nasa would not have initiated the countdown without a plan to get everyone back to Earth unharmed. Yet Davis is at the controls, already firing us out of Europe’s orbit on an undefined trajectory, with a shaky grasp of the laws of political gravity.