In this lesson we have a great principle—probably the most important major principle of psychology! We have learned that our thoughts and actions toward others resemble an electric magnet which attracts to us the same sort of thought and the same sort of action that we, ourselves, create.
We have learned that “like attracts like,” whether bodily action. We have learned that the human mind responds, in kind, to whatever thought impressions it receives. We have learned that the human mind resembles mother earth in that it will reproduce a crop of muscular action which corresponds, in kind, to the sensory impressions planted in it. We have learned that kindness begets kindness and unkindness and injustice beget unkindness and injustice.
~ Napoleon Hill, The Law of Success (1928)