People who are insane are given special treatment with respect to the contacts they enter into. If they are so insane they don’t know what they are doing the contract isn’t binding if the other party knew or ought to have known of the insanity. Should the only question be whether there was insanity? Would that be fair to merchants? Why don’t we treat contracts with infants the same way and allow the infant to escape the contract only if the adult with whom they were dealing knew they were contracting with an infant?