What accounts for the spread of political protest and contention across countries? Analyzing the wildfire of attempted revolutions in 1848, the present article assesses four causal mechanisms for explaining diffusion, namely external pressure from a great power (such as revolutionary France after 1789); the promotion of new norms and values—such as liberalism and democracy—by more advanced countries; rational learning from successful contention in other nations; or boundedly rational, potentially distorted inferences from select foreign experiences. The patterns in which revolutionary contention spread and eyewitness reports from all sides of the ensuing conflicts suggest that bounded rationality played a crucial role: cognitive heuristics that deviate from fully rational procedures drew attention to some experiences but not others and induced both challengers and defenders of the established order to draw rash conclusions from these experiences, particularly the French monarchy's fall in February 1848. My study also shows, however, that other factors made important contributions, for instance by preparing the ground for the wave of regime contention.