Dr. Kahneman’s research was best known for debunking the notion of “homo economicus,” the “economic man” who since the epoch of Adam Smith was considered a rational being who acts out of self-interest. Instead, Dr. Kahneman found, people rely on intellectual shortcuts that often lead to wrongheaded decisions that go against their own best interest. His death was confirmed by his stepdaughter Deborah Treisman, the fiction editor for The New Yorker. She did not say where or how he died. Daniel Kahneman, an Israeli-American psychologist and best-selling author awarded a Nobel Prize for research that upended economics — as well...