Concorde fallacy

Name given by evolutionary biologists to a form of suboptimal behaviour found among wasps and policymakers. Certain species of wasp are observed to defend their nests with an amount of energy proportionate to the amount they have spent on building the nest. It would be more efficient for them to defend them with an amount of energy proportionate to the cost of an alternative and the strength of the aggressor. Likewise, wasteful public expenditure on the supersonic aircraft Concorde was defended on the grounds that a great deal had already been spent. But this argument is fallacious. What has been spent has been spent, regardless of what happens now. Spilt milk cannot be unspilt. Spending on Concorde should have been judged by the expected value of the extra spending being contemplated, and on that alone.

The Concorde fallacy is extremely widespread in human reasoning, with the result that policymakers who commit it are rarely punished for doing so.