I can understand why some reasonable people want to leave the EU. What’s more puzzling is why so many think it is worth the bother. Is it worth dividing the country, triggering a political crisis worse than 2008, causing a “toxic period” in politics, and stealing all cognitive bandwidth from countless other issues?

In truth, though, there is an answer here. It is precisely because Brexit is proving to be so expensive that its supporters will continue to value it so highly.

One reason for this was discovered back in 1959 by Elliott Aronson and Judson Mills. They got female undergraduates to undergo initiation ceremonies (pdf) into a college sorority. For some, these ceremonies were mild, but for others they consisted in asking students to read out obscene words to the group (which was embarrassing for young women in the 1950s). They found that:

Subjects who underwent a severe initiation perceived the group as being significantly more attractive than did those who underwent a mild initiation or no initiation.

This corroborated their prior belief that “persons who go through a great deal of trouble or pain to attain something tend to value it more highly than persons who attain the same thing with a minimum of effort.”

Dan Ariely has called this the Ikea effect (pdf). If we go to the trouble of schlepping to Ikea and then assembling one of its bookcases, we value the product more. As he says in Predictably Irrational: “The more work you put into something, the more ownership you begin to feel for it.” John Locke’s idea that we come to own something by mixing our labour with it might be bad law and terrible history, but it’s beautiful psychology.

By the same token, the very fact that Brexit is proving so hard to achieve will cause its supporters to value it so much. Far from applying the very wise Cushnie principle - “it’s not worth the bother” – they are as determined as ever to see Brexit through.

Aronson and Mills thought that what goes on in these cases is a form of dissonance reduction – an attempt to reduce the conflict between two apparently conflicting beliefs. So, if you believe “Brexit is good” and “Brexit is hard to achieve”, you reconcile these two by thinking that Brexit is so valuable that it’ll be worth all the sacrifices.

As Robert Cialdini says in Influence, we have a huge desire for consistency – no only to hold consistent beliefs at the same time, but to have consistent beliefs over time:

Once we have made a choice or taken a stand, we will encounter personal and interpersonal pressures to behave consistently with that commitment. These pressures will cause us to respond in ways that justify our earlier decision. (Influence, p57)

Marketing departments, of course, know all this. Financial advice and university textbooks are expensive not only in an attempt to signal quality, but also to induce choice-supportive bias – to get us to think “this must be good: I paid so much for it.”

Critics of mainstream economics might see this as grist to their mill. Orthodox micro assumes that for individual consumers price and marginal utility are separate things. They are, for expected marginal utility. For experienced marginal utility, however, they are not: a high price can give us higher experienced marginal utility.

This, though, is a side-point. The main point is a depressing one. The high cost of Brexit, far from being a reason not to leave the EU, is only entrenching Brexiters' opinions. Which means that the divisions Brexit is causing will last for years.