Everything in politics is harder than it looks. Theresa May is not the first person to reach high office, only to discover that the skills used for getting a job are insufficient for doing it well. Boris Johnson – unlike his boss in most ways – is in a similar bind. He is a more gifted performer than the prime minister, but loquacity isn’t competence.

The foreign secretary’s talent for bombastic phraseology and self-aggrandising frivolity is the opposite of what is required of a chief diplomat. Johnson isn’t good at his current job and is bored with it. The proof is in the essay he published last week, setting out a personal account of what Brexit should mean. It can be interpreted only as a challenge to the prime minister, who is due to outline her own prospectus in a speech in Florence on Friday. Whatever she says will be parsed alongside the pre-emptive rival text. That reinforces the impression of a government unsure of what it wants from a process over which the clock ominously ticks.

Spreading confusion this way can’t possibly strengthen Britain’s negotiating position. Johnson knows as much, and doesn’t care. He is concerned with a different position. In drafting her speech, the prime minister has in mind European leaders, who will decide next month whether talks on Britain’s divorce terms have progressed enough to permit the opening of a second phase covering future trade. Johnson’s dissertation has in mind those Tories who prefer not to dwell on the perspective of other EU leaders, since any honest appraisal of foreign interests spoils the story that Brexit is a marvellous gift that the British government can unilaterally bestow on its citizens.

Johnson’s cheerleaders depict his intervention as a vision for the future, pointing to his breathless digressions on infrastructure and the wonders of science. In truth, Johnson is facing backwards – not in the nostalgic spirit of Ukip, memorialising empire and 1950s ethnic homogeneity, but in the spirit of 2016 and a leave campaign that dodged questions about the practicality of what it was advocating. No wonder he misses it, his ego’s finest hour.

The mere fact of Boris endorsing Brexit led the news for days because a decision of paramount national importance had been subsumed into an internal Tory party drama – what Vince Cable acidly described at the Liberal Democrat conference yesterday as “public schoolboys reliving their dormitory pillow fights”.

Johnson is still playing games. May is not. The standard account of cabinet tribes marks out “soft” and “hard” Brexiters. It pits those, such as Philip Hammond and Amber Rudd, who seek maximum continuity with existing structures, and are prepared to pay for it, against those, such as Liam Fox and Johnson, who countenance sudden rupture. The prime minister is depicted straddling the gap, thrown off balance by humiliation in the spring election.

There is a better distinction. Some Tories have moved on from the question of what needs doing – the referendum answered that with the single word “leave” – and are applying themselves to the problem of how it might be done: how to protect industries that rely on the single market; how to organise the Irish border; how to support agriculture without EU subsidy. Others shrink from that challenge. They find comfort in the saccharine simplicity of restating the original cause. “Hard” Brexit is the place to which some Tories retreat to avoid getting their hands dirty with compromise. If things go wrong, they can blame the pragmatists for sullying the dream.

The prime minister wasted a year indulging that tendency. One May loyalist describes frustration in cabinet committees when trying to get radical Brexit ministers to focus on detail. Every obstacle is belittled as a symptom of weak faith; every workaround is treated as a trap laid by unrepentant Europhiles seeking to abort the whole thing. No assurance by ex-remainers that they have accepted the referendum is trusted. This leads to a vicious cycle: the only people in government prepared to engage with the question of how Brexit might work are those who didn’t vote for it, which reinforces the zealots’ suspicion that the “softies” are closet saboteurs.

David Davis presents a unique frustration. The Brexit secretary sounds supportive of the pragmatists in private, but dares not cross lines drawn by the fantasists in public. Like May, he has a job that demands solutions to hard problems but, like Johnson, his ambition requires concealment from a core Conservative audience of how difficult it all is.

That tension partly explains a curious change in Whitehall personnel this week. Olly Robbins had been the top civil servant at the Brexit department under Davis, and also Downing Street’s EU point man, reporting to May. He now relinquishes the former cap to devote himself wholly to representing the prime minister.

The only people in government prepared to tackle the question of how Brexit might work are those who didn’t vote for it

There are conflicting accounts of why this happened and at whose instigation. Robbins and Davis were not bosom companions but had a functional working relationship. A good explanation is that May feels control over Brexit bleeding away, and needs reassurance that her writ runs along the straightest line through Whitehall and into the Brussels negotiating chamber. She cannot have Robbins serving a second master.

This is a small twist in a long tale, but it expresses that bigger tension between practice and theories of Brexit. Reality is coming on hard and fast. May’s true allies in confronting it are the people who warned all along that the impact would hurt. But she has a cabinet packed with people who insist that the collision is avoidable.

You can tell them by the Johnsonian way they twist queries about how it is done into rehashed arguments about why it must be done. And she has a party that prefers a game of hunt-the-saboteur to the boring homework of negotiation. It shouldn’t come as a surprise that extricating the UK from EU membership is harder than advertised, but the obstacle to doing it safely is not those who said it shouldn’t be done. That battle was lost last year. The source of sabotage is those Tories who now prefer the idea of Brexit to the real thing.

• Rafael Behr is a Guardian columnist