There are Nudge Units and pronouncements upon human economic fallibility all around us. Us folks don;t, in fact, approach the universe in the supremely calculating manner than certain economic models insist we do.

Except of course the models don’t insist, they just explore what would happen if we did. All of interesting economics is in explaining what happens when behaviour deviates from the model which is why we use such models. So that we can explore the deviations from them.

However, despite all this attention paid to such fallibilities we’re about to see the most monstrous display of the Sunk Cost Fallacy:

Conservative MPs are lining up to denounce HS2 in the Commons after more than 100,000 members of the public secured a debate on scrapping the high-speed rail line.

Senior Tories are preparing to urge ministers to put the project "out of its misery" as they point to spiralling costs and a shift to working from home as evidence that it should be cancelled and the £98 billion budget distributed elsewhere.

We know what’s going to happen next. There will be an outburst of shouting. But, we’ve already spent £1, £1 billion, £10 billion. If we don’t go on then all that will be wasted!

Sunk costs are sunk costs. This is money, those are resources, that have already been applied to this scheme, whatever it is. Whether we proceed with the scheme or not we will never get those resources, that money back. So, that we’ve already spent the cash is an irrelevance to the decision about whether we should proceed.

Our decision should be based upon whether the benefits from proceeding - from our current starting point - are greater than the costs of doing so. The past is indeed past and our decisions are about our path into the future that is.

We really are going to have multitudes shouting that we must not waste what is already spent. The problem with that shout being that what is already spent is already wasted. No decision can bring it back.

Now, whether HS2 should be cancelled or not is another matter. We have, often enough, pointed out that it should never have been started and recent changes just make that more true. But the welcome cancellation isn’t the point here. Rather, that the decision must be taken using the right metrics.

Sunk costs are sunk costs. What has already been spent is irrelevant. The decision must rest upon what is to be gained from spending how much given our current starting point?

This is politics so it won’t be but then bully for politics as a method of spending money then.