The Sony Walkman is one of the most successful electronic products of all time. After the introduction of the Philips compact cassette in 1963, by the 1970s the size of a cassette player had settled at about the size of a trade paperback. The truth was that nobody really saw the need to make it any smaller. So when Sony introduced the pocket-sized Soundabout, later called the Walkman, it seemed a clever concept that would never catch on. Unlike other cassette players in 1979, the Soundabout had no loudspeaker, delivering sound through stereo headphones. Even Sony's marketing department did not expect it to sell. Although the Japanese liked it, in the United States consumers were put off by the $200 price tag.

The Walkman II, introduced in 1981, was smaller, simpler, and much cheaper. Within a couple of years other manufacturers had entered the market. Whatever they called their products officially, competitors'...