To identify the economic stars of the future we should abandon the habit of extrapolating from the recent past and lumping wildly diverse countries together. We need to remember that sustained economic success is a rare phenomenon.   As an era of easy money and easy growth comes to a close, China in particular will cool down. Other major players including Brazil, Russia, and India face their own daunting challenges and inflated expectations. The new "breakout nations" will probably spring from the margins, even from the shadows. Ruchir Sharma, one of the world’s largest investors in emerging markets for Morgan Stanley, here identifies which are most likely to leap ahead and why.