Empathy—the ability to relate to and understand the perspective of others—is sometimes completely absent and at other times difficult to sustain. “There’s a school of thought that suggests that empathy is automatic and effortless,” says Michael Inzlicht, a psychology professor at the University of Toronto. Yet according to a new study led by Inzlicht, this conception might not be accurate. People, it turns out, may opt against empathy if the mental effort needed is too high. In other words, empathy could be an on-off switch that’s easier left in the off position.