Dhammapada

What you think, you become

Earliest we can find

This is the earliest source we can find for the idea. Said again in 4 books on our list: Marcus Aurelius, Meditations (c. 175), James Allen, As a Man Thinketh (1903), Dale Carnegie, How to Stop Worrying and Start Living (1948) and Norman Vincent Peale, The Power of Positive Thinking (1952).

1. “All that we are is the result of what we have thought: it is founded on our thoughts, it is made up of our thoughts.”