In July 2016, on the eve of his appointment as secretary of state for Brexit, David Davis predicted that the whole thing would be a doddle. Brussels would cater to Britain’s needs and the prime minister would simultaneously negotiate “a free trade area massively larger than the EU”. Within a year, Davis had changed his tune. It was complicated, he conceded. In June 2017, he told an audience of business leaders that the intricacies of the negotiations “make the Nasa moonshot look quite simple”. In July 2018, Davis resigned.

He is not the only gung-ho Eurosceptic to meet a steep learning curve in government. His successor, Dominic Raab, is at a different stage on the journey, but the trajectory looks familiar. His speech to Tory conference this year had the swagger of the Brexit buccaneer who has yet to experience the pitch and roll of open water. “If the EU want a deal, they need to get serious,” he said. He did not specify what aspect of the continental position was, in his eminent opinion, unserious.

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Last night, at a tech industry event, Raab admitted that his grasp of the detail had been upgraded with some salient facts – such as the importance of the Channel to commerce with Europe. “I hadn’t quite understood the full extent of this,” he said. “But if you look at how we trade in goods, we are particularly reliant on the Dover-Calais crossing.”

It is no longer surprising that people who were once confident that Britain had nothing to lose by leaving the EU neither understood what Brexit meant in practice, nor thought to ask. (That doesn’t make it any less dismal that the rest of us are expected to live with the consequences of their incuriosity.) It turns out that the states of being a Brexit ideologue and of being a responsible minister are not really compatible. Ardent leavers who join the cabinet are soon handed a menu of unpalatable choices. They turn queasy at the diet of sticky, granular detail. It wears them down until they are forced to soften their position, change the subject or quit.

Boris Johnson, like Davis, chose the easy route: back to the comfort of moaning from the sidelines. Michael Gove discovered a crusading interest in the fate of plastic in the ocean that apparently excuses him from any duty to explain why promises made by the campaign he fronted will not be delivered. If Andrea Leadsom and Chris Grayling think Brexit has turned out as well as they once thought it would, they aren’t saying so. Liam Fox has had a jolly old time jetting around the world, meeting deputy trade ministers and being told that, yes, there is a free trade agreement to be signed with the UK just as soon as it has sorted out its future status with the EU (or in the case of the US, just as soon as it is prepared to surrender to every one of Donald Trump’s capricious demands). Fox is personally quite loyal to Theresa May, which is a rare thing in the cabinet. Plus, the ministerial car can shield the delicate ego from blows that might otherwise be inflicted by having a non-job.

A remain-supporting former cabinet minister once told me of frustration in dealing with pro-leave ministers in the early months of the May government. When presented with technical Brexit-related issues in their departments, the true believers would cry foul, saying obstacles were being blown out of proportion, or that the real problem was a lack of will and the solution was more faith. Thus the ludicrous situation arose where the people most seriously engaged in trying to imagine a way forward – the prime minister and the chancellor – had both voted remain. David Davis was the exception, since his job allowed no ducking of difficult questions. He had to confront facts and, when he resisted, the facts won.

Now Raab occupies Davis’s old seat, trying to bring Brexit back from its two-year journey to the moon. Re-entry into reality is proving tricky. The myths and the cocksure rhetoric are burning off on contact with the Earth’s atmosphere. It is possible the whole thing can be brought home in one piece, but also that it breaks apart completely, revealing the fundamental design flaw: this rocket was not designed with a safe landing in mind.

• Rafael Behr is a Guardian columnist