Principle No. 2 of the Beatles’ success is: Develop your products and services gradually, and give your 100th customer as much attention and enthusiasm as your first. Most rock bands consistently play the same kind of music, and the songs are similar. The Beatles took a different path. From album to album they changed the nature of their songs, and in many ways. They came up with new song themes, melodic lines, introduced new arrangements and previously unused instruments. Albums with such disparate songs as “Yesterday” and “Revolution” sold more than a million copies in a decade. The Beatles, in
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