Answer: Because Y's failure to notice the leaky faucet means that he did not justifiably rely on X's "misstatement."
Explanation: Ben may be unable to rescind on the basis that, upon the sale of the property, the leaky faucet is as not intentionally hidden from Ben's notice. If during the property inspection, the leaky faucet was noticed by Ben, and Colleen gave a false statement about the faucet in other to conceal the impairment, then Colleen would have been deemed to have made Ben rely on a false statement and thus making a rescind by Ben would have been possible.