The piece of string has been mistaken for a wallet. Although Maitre Hauchecome is innocent, his enemy saw him picking up something on the ground. When the wallet is reported as lost, Maitre Malandain reports that Maitre Hauchecome was seen picking up the wallet when in fact he was only picking up a piece of string.
Although there is no truth in Maitre Malandain's story, the whole town believes him. No one can imagine that Maitre Hauchecome would be only picking up a piece of string.
The moral of the story is that it does not pay to be to stingy. It is not wise to be too conservative. A piece of string with no value becomes confused with a wallet containing 500 francs. If only Maitre hauchecome had wlaked on by the piece of string, his reputation would not have been ruined in one single day and all for the price of a piece of string.