In 1950, Earl Nightingale was inspired by the words “we become what we think about” in Napoleon Hill‘s book Think and Grow Rich around the same time he bought an insurance agency. He provided weekly motivational speeches to the agency’s sales staff. In 1956, he recorded a motivational speech to be played while he was on vacation. Nightingale’s employees spread word of the speech, and demand for the recording grew so large that he and friend Lloyd Conant formed the Nightingale-Conant Corporation to manage sales.

Here is a good collection of some of his speaches, audio only but great to listen to.
https://archive.org/details/06-great-expectations/