In Dattatreya's life, he has spoken of how he had attained Jnana through observing nature around him. In that he mentions, whatever a human thinks of constantly, he attains that form by citing an example.
The Bhringi or the BEETLE catches hold of a worm, puts it in its nest, and gives it a sting. The poor worm, always fearing the return of the beetle and sting, and thinking constantly of the beetle, becomes a beetle itself. Whatever form a man constantly thinks of, he attains in course of time that form. As a man thinks, so he becomes. I have learnt from the beetle and the worm to turn myself into Atman by contemplating constantly on It and thus to give up all attachment to the body and attain Moksha or Liberation."