A landmark social-science thesis began as an unverified personal hunch.

Evidence

I began idly to explore what statistical evidence I could find that might reveal trends in civic engagement in America, not at all sure whether hard data would substantiate my hunch. … Over breakfast that spring a generous friend, Peter Ackerman, mentioned that trends in league bowling seemed to fit my evolving generalization. — Robert D. Putnam, Bowling Alone The Collapse and Revival…, 2638