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Intelligence is the main factor, coupled with social mores. However in free markets social mobility is a given.

By what criterion do you measure success? Some people make financial success their top priority, some, spirituality, some happiness. The list is endless. Decide what is at the top of your list, what is the best way of achieving it and maintain a single minded determination to reach your goal. That way if you fall short at least you will have achieved something and you will have no cause for self blame because you will know you did your best.