What happens when you mix the efficiency and energy of the entrepreneurial world with the idealism of philanthropy? A growing number of social entrepreneurs say, you can do a world of good. But just like real entrepreneurs, more such efforts fail than succeed, and both smarts and resilience are needed for the long haul. Jonathan Lewis, author of The Unfinished Social Entrepreneur and founder of the microcredit funder MCE Social Capital and cofounder of Copia, a kind of mail-order catalogue for poor women around Nairobi, shares what he's learned over years as a social entrepreneur.