How did David Hume explain people’s belief in cause and effect?

David Hume explained that our belief in cause and effect does not arise from rational demonstration or direct observation, but rather from psychological habit and custom.123

According to Hume, when we observe two events—such as a fire and heat—we only ever perceive their "constant conjunction," meaning they have frequently occurred together in the past. We never actually observe a "necessary connection" between them.4531

Instead, the idea of necessary connection is a subjective feeling. When the mind repeatedly experiences two events in succession, it develops a habit of association. Upon perceiving the first event, the mind is compelled by this custom to anticipate the second. This internal feeling of being "carried along" or "determined" is the impression from which our idea of necessary connection is derived.415

Hume concluded that while these beliefs are not logically justified—as they rely on the unprovable assumption that the future will resemble the past—they are natural, inextinguishable propensities of human nature that are essential for survival. Thus, for Hume, custom, not reason, is the guide of life.231