According to popular mythology, the publisher Allen Lane, founder of Penguin Books, formulated his idea for a press dedicated exclusively to paperbacks while visiting a railway station. Having spent the weekend visiting his friend Agatha Christie, the famed author of Murder on the Orient Express, Lane arrived at the Exeter railway station and realized he had forgotten his book. Frustrated and facing the boredom of a long train trip, Lane tried to buy a novel at the station but found that there was nothing available that he felt worth reading. Bookless for the next few hours, he sat on the train and planned a new line of cheap, pocket-sized, and travel-worthy books, which could be sold at railway stations, grocers, and department stores. Penguin Books—and the paperback revolution—were born.
A fascinating article (and slideshow) on how Penguin revolutionized the paperback.