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A worker stands in a construction project in a favela, or shantytown, in Rio de Janeiro, Brazil. The government has helped drive down income inequality by investing in basic services like health care, education and pensions. Mario Tama/Getty Images hide caption

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Mario Tama/Getty Images

Duncan Green, author of "How Change Happens." He says of activism: "There has to be a little part of you that acknowledges doubt, ambiguity and uncertainty. You have to have room to change direction." Ben de la Cruz/NPR hide caption

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Ben de la Cruz/NPR

A 2014 photo shows shanty houses on a river bank in Jakarta, Indonesia, where Indonesian President Joko Widodo once pledged to close a fast-growing wealth gap. Bay Ismoyo /AFP/Getty Images hide caption

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Bay Ismoyo /AFP/Getty Images