When something big happens, did something big cause it? Did the cause of a pandemic have to be a big event? Was a typo in a legal document that cost millions of dollars premeditated sabotage? Does a drunk expression of affection come from romantic love for the person? If you think about these questions, you might notice that we try to estimate the nature of the cause based on observable effects. We sometimes tend to equate or match the magnitude of a cause and its effect: a thinking shortcut called the major-event/major-cause heuristic. It’s also called the proportionality bias, where we assume that effects are proportional to their causes – we show a bias to think large events are caused by large actions, and small effects have small causes. It helps us make quick judgments when we don’t know enough details.