If both sides have a mutual misunderstanding that causes the contract to misallocate costs or risks, fairness requires that the misallocation be corrected unless the contract shows an intent to allocate the risk. Not all legal systems recognize a concept of "equitable mistake", but I don't think there's any serious disagreement that it's equitable.

A classic example would be two parties who each believe that a ship sunk in a particular place and negotiate a fixed-cost contract to retrieve the ship for a specified fee. If it turns out the ship was elsewhere and is therefore much more expensive to recover, fairness requires the fee be adjusted appropriately. This, of course, only applies if the party seeking the re-adjustment is not comparatively more at fault for the incorrect information. It also only applies if the contract doesn't show an intent to allocate the risk that the information was incorrect to the party being paid to recover the ship.

This situation is analogous. Both parties incorrectly (arguably, equally negligently) believed Starfish's high-interest loan model was sound. There's no evidence in the contract that the risk that the business model was fundamentally unsound was intended to be allocated to Patrick. So the contract cannot equitably be enforced as drafted because a situation not foreseen by the contract came to be. The risk of the unsound business model has to be allocated among the parties somehow, the contract doesn't specify how to allocate it, equity demands it be split.

Again, not all legal systems recognize a doctrine of equitable mistake. Some will insist a contract be enforced as written even if a risk that contract fails to allocate (due to a common mistake of fact shared by both partied to the contract and forming part of the basis of the actual "mental" agreement) materializes unless that makes complying with the contract impossible. But there are very few people who think this is actually fair.