The Crow and the Swan

A Crow was filled with envy on seeing the beautiful white plumage of a Swan, and thought it was due to the water in which the Swan constantly bathed and swam. So he left the neighbourhood of the altars, where he got his living by picking up bits of the meat offered in sacrifice, and went and lived among the pools and streams. But though he bathed and washed his feathers many times a day, he didn't make them any whiter, and at last died of hunger into the bargain.

You may change your habits, but not your nature.