So, I've been sick.

From here:

"Look at the first edition of AD&D. It was a relatively complex game, but it has lots of causal players -- because while its rules were complex, you really did not have to know many of them to play. A lot of rules knowledge -- let alone system mastery -- wasn't needed to play. The only person who really needed a good knowledge of the complex rules of first edition AD&D was the GM."