Human behavior is best explained by tracing the economic, social, and moral incentives acting on people, because people respond predictably to the rewards and penalties they face. When outcomes look puzzling, the explanation usually lies in a hidden incentive structure rather than in character or stated intentions.
In Japanese sumo, top-division wrestlers fight 15 bouts and face demotion with fewer than eight wins; a 7-7 wrestler facing an 8-6 opponent in the last match wins about 80% of the time despite being the weaker fighter. Levitt infers match-fixing: the wrestler who already has eight wins throws the bout because the marginal win means everything to his opponent and little to himself.
To find hidden cheating, ask what the data would look like if cheating occurred, then search for that signature. In Chicago schools, teachers who altered answer sheets left a telltale pattern: hard questions at the end of a section answered correctly more often than easy ones at the start, revealing erased-and-corrected blocks.
Experts and insiders profit from holding information their counterparts lack, whether a real-estate agent nudging a client toward a quick sale or the Ku Klux Klan guarding secret rituals. Expose or distribute that information and the advantage collapses, which is why transparency can neutralize power more effectively than confrontation.
Levitt argues that the 1973 legalization of abortion reduced crime roughly two decades later, because children who would have been unwanted were disproportionately at risk of becoming criminals. He frames this as one contributing factor identified in the data, not the sole cause of the crime decline.