Hegel's doctrine — die List der Vernunft — that Reason accomplishes its purposes not through direct intervention but through the passions, ambitions, and particular interests of individuals who believe they are pursuing their own ends while unwittingly serving a universal they cannot see.
The cunning of Reason is Hegel's account of how historical development occurs without requiring that individual agents understand or intend the pattern their actions compose. Reason does not announce itself. It does not issue commands. It works through indirection — through the passions, ambitions, fears, and particular interests of agents who believe themselves to be pursuing their own ends and who are, in fact, the unwitting instruments of larger historical movements. Napoleon pursued glory; he was the instrument of the rationalization of European political institutions. The early modern merchants pursued profit; they were building the infrastructure of a global economic system no individual designed. The individual is real, the passion is real, the particular purpose is real — but the aggregate effect of millions of such particular purposes is a pattern that transcends any participant's comprehension.