In 1960, while they were still an unknown high school rock band, the Beatles went to Hamburg, Germany to play in the local clubs.

The group was underpaid. The acoustics were terrible. The audiences were unappreciative. So what did the Beatles get out of the Hamburg experience?

Non-stop hours of playing time, practice, and immediate feedback forced them to get better. That's the key difference that rose The Beatles to the top, according to Malcolm Gladwell in his book Outliers .

As the Beatles grew in skill, audiences demanded more performances -- more playing time. By 1962 they were playing eight hours per night, seven nights per week. By 1964, the year they burst on the international scene, the Beatles had played over 1,200 concerts together.