Why are there so few people who are successful in multiple disciplines?

People like Arnold Schwarzenegger who was former Mr. Olympia, famous actor, governor of California, savvy businessman, etc etc. You rarely see people who are professional athletes, have a PhD or Masters degree, and also run several successful businesses, or a similar variation of that like a famous musician, a... show more People like Arnold Schwarzenegger who was former Mr. Olympia, famous actor, governor of California, savvy businessman, etc etc. You rarely see people who are professional athletes, have a PhD or Masters degree, and also run several successful businesses, or a similar variation of that like a famous musician, a model, and also medical doctor neurosurgeon
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