"You become what you think about. The law of concentration states that "anything you dwell upon grows in your reality." What you habitually think about eventually becomes a part of your character and your personality. You cannot harbor one kind of thought and experience a different kind of existence.

Just like a magnet attracts iron filings, you attract whatever is consistent with whatever you are thinking about most of the time." 

— Brian Tracy

Author, The Power of Self Confidence.