Let’s have a quick look at this. Both quotes are closely related.
Henry Ford (1921)
“Whether you think you can or you can't, you are right.”
~ Henry Ford
Henry Ford (July 30, 1863 – April 7, 1947) was an American industrialist, the founder of the Ford Motor Company, and the sponsor of the development of the assembly line technique of mass production.
Although Ford invented neither the automobile nor the assembly line, he developed and manufactured the first automobile that many middle class Americans could afford. In doing so, Ford converted the automobile from an expensive curiosity into a practical conveyance that would profoundly impact the landscape of the 20th Century. His introduction of the Model T automobile revolutionized transportation and American industry. As the owner of the Ford Motor Company, he became one of the richest and best-known people in the world. (Source: Wikipedia)
Napoleon Hill (1937)
“Whatever the mind can conceive and believe, it can achieve.”
Napoleon Hill (1883 – 1970) was an American author and impresario who became an early producer of personal-success literature. At the time of Hill's death in 1970, his best-known work, Think and Grow Rich (1937) had sold 20 million copies. Hill's works insisted that fervid expectations are essential to increasing one's income. Most of his books were promoted as expositing principles to achieve "success". Hill was an advisor to two presidents of the United States of America, Woodrow Wilson and Franklin Delano Roosevelt. (Source: Wikipedia)
Focus on what you want to do and not on what you cannot do.