Explain SMBC — the wiki for Saturday Morning Breakfast Cereal

This comic satirizes radical philosophical skepticism about causation. A man with glasses confidently declares that events cannot be causally connected and that all we have are subjective correlations -- a position associated with an extreme reading of philosopher David Hume's skepticism about cause and effect. In the next panels, the other man turns off the light (click), there is a loud "BANG!" in the darkness, and when the light comes back on, the skeptic is clutching a bloody wound on his arm.

The punchline comes when the man who flicked the switch asks, "What'd the darkness do to your arm?" -- sarcastically attributing the injury to the darkness rather than to the obvious cause (being shot). This throws the skeptic's own logic back at him: if we cannot infer causal connections, then we cannot say the gun caused the wound, and attributing it to the darkness is just as valid. The comic mocks armchair philosophical positions that deny obvious real-world causal relationships by showing how absurd and dangerous such thinking would be in practice.