When learning the relation between a cause and effect, how do people control for all the other factors that influence the same effect? Two experiments tested a hypothesis that people focus on events in which the target cause changes and all other factors remain stable. In both four-cause (Experiment 1) and eight-cause (Experiment 2) scenarios, participants learned causal relations more accurately when they viewed datasets in which only one cause changed at a time. However, participants in the comparison condition, in which multiple causes changed simultaneously, performed fairly well; in addition to focusing on events when a single cause changed, they also used events in which multiple causes changed for updating their beliefs about causal strength. These findings help explain how people are able to learn causal relations in situations when there are many alternative factors.