One formula predicts inequality will keep rising almost automatically: r > g

In Capital in the Twenty-First Century, economist Thomas Piketty compiled centuries of tax records across many countries and argued that whenever the return on capital (r) outpaces overall growth (g), wealth concentrates in the hands of those who already own assets, since their fortunes compound faster than everyone else's wages grow. He argued this has been the historical norm, briefly interrupted only by the wars and taxes of the 20th century. The book became an unlikely bestseller.

— Thomas Piketty, Capital in the Twenty-First Century — 2013
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