If you treat an individual as he is, he will remain how he is. But if you treat him as if he were what he ought to be and could be, he will become what he ought to be and could be.

This quote means that if you accept someone for who they currently are, they will not change or make any improvements. However, if you treat them as you think they should be, they can make the effort to change and improve themselves to become the person that you think they could be. In other words, if you encourage someone to be the best version of themselves, it can inspire them to try and make improvements.