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Self-determination theory, developed in the 1970s and 1980s by psychologists Edward L. Deci and Richard Ryan, grew out of a 1971 experiment with the Soma cube, a 3D puzzle students enjoyed. Over three sessions, one group was paid a dollar per solved puzzle in the second session, then told the money had run out. During an eight-minute free choice period watched through a one-way mirror, the formerly paid students played with the puzzle far less than at the start, while the unpaid group kept playing. Deci found the same drop with college newspaper writers paid 50 cents a headline, and a 1977 study by Pritchard found it with chess problems. Verbal praise, by contrast, increased motivation.

The theory names three universal needs: autonomy, competence and relatedness. Its sub-theory, organismic integration theory, ranks extrinsic motivation from external regulation through introjected, identified and integrated regulation, explaining how people come to own tasks they do not enjoy. The episode applies this to dull lessons, Sudbury schools, prediabetes diets in rural Uganda and urban South Africa, and college drinking, then covers causality orientations and critics such as Steven Reiss, who argued that the line between intrinsic and extrinsic motivation is often blurry.

• Money is said to shift the locus of causality, so the activity starts to feel controlled rather than chosen.
• Autonomy in this theory means acting in line with one’s own values, not isolation; volunteering to help a friend move counts as autonomous.
• Giving students a clear reason why a dull lesson mattered moved them toward identified regulation and more interest.
• In the prediabetes studies, guilt-driven motivation was linked to worse diet adherence, while peer support and feeling competent helped.
• Students low in autonomy were more likely to drink heavily under peer pressure for extrinsic reasons.