The law has long recognised a right to recover an enrichment transferred on a consideration which has failed. However, the consideration has to fail totally. Much ink has been spilled arguing that the limit is a bad one. Less has been written about quite what a total failure of consideration actually is. In this paper, it is argued that the best understanding of the total failure rule is that it prevents restitution when the failure is insubstantial; only substantial failures justify restitution. This shows that the limit is integral to the justification of the award of restitution.