The Impostor explained simply

A certain man fell ill, and, being in a very bad way, he made a vow that he would sacrifice a hundred oxen to the gods if they would grant him a return to health. Wishing to see how he would keep his vow, they caused him to recover in a short time. Now, he hadn't an ox in the world, so he made a hundred little oxen out of tallow and offered them up on an altar, at the same time saying, "Ye gods, I call you to witness that I have discharged my vow." The gods determined to be even with him, so they sent him a dream, in which he was bidden to go to the sea-shore and fetch a hundred crowns which he was to find there. Hastening in great excitement to the shore, he fell in with a band of robbers, who seized him and carried him off to sell as a slave: and when they sold him a hundred crowns was the sum he fetched. Do not promise more than you can perform.