Born into poverty, Carnegie worked as a traveling salesman before he began teaching public speaking at a YMCA in New York City in 1912. His classes were extremely successful, and he was soon lecturing to packed houses. To standardize his teaching methods, he began publishing pamphlets, which he collected into book form. His hugely popular How To Win Friends and Influence People won him a national following. How many people are said to have taken his courses during his lifetime?