Nothing about Brexit means it can only happen on 29 March 2019. There is no rare alignment of the planets to make that a uniquely auspicious date for leaving the EU. Britain’s relationship with its nearest allies is not settled by astrology. The March deadline is simply a feature of the negotiating apparatus and, as the prime minister conceded in parliament yesterday, it can be moved. Leaving in April or June is still leaving.

It is the psychology of letting a deadline slip that makes Theresa May’s concession so significant. If Eurosceptics were interested in divorce on civil terms they would endure a short technical postponement to get it right. They would not resent the vote on a deferral that May has offered to MPs in the event that her deal is rejected. Article 50 extension has looked inevitable for weeks, if the objective is smooth passage to whatever comes next. So it is instructive that so many Brexiteers hate the idea.

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Their declared objection is that the public has commissioned a job and wants it done on time. But there is no such thing as finishing Brexit. Even if May’s deal forms the basis of an orderly withdrawal, it initiates more negotiations on the long-term relationship. In the best-case scenario, those talks are completed within a 21-month transition period. The dynamics of an evolving European project mean that Britain will then for the foreseeable future be loitering in Brussels ante-chambers, trying to resolve issues arising from its weird status as a former member of the club.

A dirty secret in the leaver camp is that there is no “clean Brexit”, although it is a clever rhetorical trick to suggest one. The vote to leave the EU contained a desire to be rid of the whole European question. Much of the visceral appeal of Brexit was in its aura of simplification. It promised to prune back the tendrils of foreign meddling, to make a tidier, more sovereign land. It is a kind of Marie Kondo doctrine of national de-cluttering to liberate the inner joy of clean-lined Britishness. It was only remainers who fixated on the technical complexity of the task and, since they didn’t think it should be done at all, their objections were easily dismissed as bogus excuses for not getting on with the task.

But Brexit is irredeemably complex. There is no tidy way to do it, and the messiest version of all is the one that the hardest Brexiters advocate – quitting without a comprehensive agreement. This is routinely called the “no deal” scenario, but that is a misnomer. Only if Britain wants to be more isolated than North Korea will there be literally no deal.

In every other model there are deals: on planes landing; on people and goods crossing borders; on mutual recognition of standards and qualifications; on extraditing villains and exchanging students; on the weft and the warp of modern civilisation. The difference between a grand treaty struck under the article 50 process and multiple emergency protocols, hastily concocted under circumstances craved by the hardest Brexiters, is that in the latter case, Britain would have to step out from behind the table in Brussels and negotiate on its knees.

Facebook Twitter Pinterest Theresa May leaving 10 Downing Street. Photograph: Leon Neal

The things that Tory backbenchers currently dislike about May’s plan (principally the Irish “backstop”) have come about as a consequence of asymmetric power. The UK has not been able to undermine the solidarity, or overcome the combined diplomatic muscle, of a 27-nation bloc. That imbalance becomes more pronounced once the article 50 period expires.

Bluffing stops when the cards are face-up on the table. May appears to understand this logic. She knows that the country is poorly equipped for an overnight severance of continental ties, so why wait so long to admit it?

Decrypting the prime minister’s motives is generally a waste of time. Cabinet ministers who have worked closely with May for years say they have no access to the private realm of her calculations. Senior officials doubt that there is a hidden strategic intelligence behind the eyes and describe her simply surviving each day as it comes. May has a fanatical devotion to the idea of fulfilling her duty, but that could mean avoiding national disaster or honouring the pledge to end EU membership on the date and on the terms that have been promised. The two imperatives pull in opposite directions.

At the core of the paralysis is the fallacy of the One True Brexit. This is the mythical deal that avoids economic disturbance while convincing ardent leavers that their demands have been met. This cannot exist because the disruption itself – the sound of fabric tearing and glass breaking – is what many Brexiters crave. Stable transition defers the gratification of instantaneous release. But it is also in the nature of Brexit, even in its hardest form, that the moment of release is illusory. It is a process, not a destination. The article 50 timetable gives structure to the first phase but it never offered resolution. The highest point for leavers, the purest elation, was in the early hours of 24 June 2016, when the referendum result was declared. The trajectory since then was towards failure. Disappointment was coded into Brexit’s political algorithms.

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This matters especially in the context of calls for another referendum. The core objection is that posing the question again is an affront to leave voters, and that they would be betrayed if remain won a rematch. That is indeed a risk, but it must be balanced against the cost of capitulating to hardline Brexiters who are determined to be betrayed and to stir up public rage under any circumstances. Even if they get exactly what they say they want – total, immediate detachment from Europe – they will blame the ensuing chaos on remain-supporting ministers and civil servants for failing to make adequate preparations. Emergency deals required to end the chaos would then be denounced as capitulations to Brussels.

There is no variant of the future in which Boris Johnson or Jacob Rees-Mogg declare themselves satisfied with the outcome of Brexit and magnanimously seek reconciliation with its critics. Grievance is the raw material they need to fuel their politics, and Euroscepticism is the mine where they extract it. They will not shut the facility down to celebrate Britain leaving the EU. Europe will always be there on our doorstep, brazenly existing, flaunting its continentalism in our faces, and the Brexit hardliners are impatient to move on to the next phase of their betrayal.

That’s why they find the thought of delaying the departure date so unbearable. Adjusting the deadline sustains the search for practical solutions. It keeps alive the idea of compromise, and that is what most offends the true spirit of Brexit.

• Rafael Behr is a Guardian columnist