A decision can be reckless and unavoidable as a film can be lousy and underrated. When David Cameron committed to a referendum on Britain’s place in the EU three years ago, allies of the prime minister — especially his nearest, George Osborne, chancellor of the exchequer — feared for their Conservative party. Economists anticipated an expensive chill on confidence and investment. Sticklers for representative democracy pictured a tawdry, unreflective campaign.

Their every dread has transpired, and even they did not expect a further problem that any advertising executive could have seen coming. A proposition, however barmy, gains a spurious credibility when offered in a side-by-side choice with something else. There was never a clamour to leave the EU. But once exit was tabled as an official option it attained a rough parity of esteem with the status quo, and not just because broadcast media had to give each side equal weight. It is hard to damn a course of action as unthinkable when you have just opened it to the country. The vagaries of choice architecture should engage politicians as much as the peddlers of washing powder and brands of cola.

A naive referendum, then, that has left Britain with a material chance of exit. Yet it made all the sense in the world. Without that pledge, Mr Cameron would certainly have succumbed to mutinous forces in his party before the 2015 general election. The Tories would have fallen to rightwing leadership. A referendum would have been held eventually anyway, most likely by a Conservative prime minister set on leaving. All else being equal, the campaign for exit would have stood a better chance than it does this Thursday.

The burden is on those of us who opposed this referendum upon its announcement, and hate every mendacious hour of it, to say what the cloudless alternative was. It has become too easy to wonder with a huff why Mr Cameron is “putting us through this”, as though a quieter life was there for the taking.

A referendum was always going to happen. There was too much subterranean pressure — too much resentment of European free movement, in particular — to contain an eruption. The questions were exactly when, and under what conditions. Now, and under a pro-EU Conservative government led by a man voters hardly adore but plainly take seriously, turned out to be the tolerable answers. They could have been much, much worse.

For while Mr Cameron underrated the lure of the riskier option on a two-option ballot, the other one is still favoured to prevail on Thursday, and not because the Remain campaign has “won” the past few months or that Leavers have flubbed them.

A political campaign cannot make people think anything they are not predisposed to think. All it does is firm up thoughts that already slosh around inchoately at the back of their heads. And to the extent that campaigns have this effect, the competing sides mostly cancel each other out. So when we analyse campaigns we are analysing the margin of the margin — or, given that most voters have made up their minds before the campaign commences, the margin of the margin of the margin.

What matters are the fundamentals, and these are understood well enough. The most impressive political analyst in the land is not employed by a newspaper. It is the median voter. The opposite of a clever fool, this person comprehends the essence of an election (or referendum) without knowing any of the detail. The essence of this referendum — the real question voters will see on the ballot — is “Do you dislike immigration more than you like economic calm?”

For an enormous share of the country, the answer is yes, and pencils will snap under the intensity with which they mark their X. But this is also a country where, according to ComRes, 68 per cent of voters would not forfeit a single pound of their income to cut immigration. It is a country where the bone-dry consumer champion Martin Lewis, a tentative Remainer, would be immortalised on Trafalgar Square’s fourth plinth if shoppers had a say. It is a country that gave Mr Cameron a majority 13 months ago because, in part, it backed him as an economic manager.

If this overrates the appeal of material continuity, and Mr Cameron loses the vote, no one will remember anything else about him. On Friday morning, he will be a wizard who revived the Tories and helped to secure two unions — Scotland’s with the rest of the UK, the UK’s with Europe — or he will be a punchline, for ever. His consolation is that, for all our exasperation with his referendum, he never had a choice but to find out.

janan.ganesh@ft.com