[ghaff]

It really depends on the use case. In general, in the commercial world, we want to be able to have transactions/contracts that can't just be voided without consequence because one of the parties thought it was a good deal at the time but it turned out not to be. On the other hand, most legal systems aren't going to enforce contracts that have ruinous effects on someone because of a simple mistake or event that no one could have foreseen.