More proof of this principle existing millennia ago are two profound quotes made by Hindu Prince Gautama Siddharta (563-483 BC), the founder of Buddhism:

“All that we are is the result of what we have thought.
The mind is everything. What we think we become.”

“The mind is everything. What you think you become.”

In the Bible there are many verses about this credence. We are told in the Old Testament in Proverbs 23:7 NASB “For as a man thinks within himself, so is he.” In the New Testament Jesus explains "So then, you will know them by their fruits." Matthew 7:20 NASB and again "Give and it shall be given to you. For whatever measure you deal out to other, it will be dealt to you in return." Luke 6:38. Paul makes it clear in Galatians 6:7 NASB “Do not be deceived, God is not mocked; for whatever a man sows, this he will also reap.” Paul promised in 2 Corinthians 9:6 NASB “Now this I say, he who sows sparingly will also reap sparingly, and he who sows bountifully will also reap bountifully.”