The first principle to bear in mind is, therefore, that the accumulation of wealth takes time: it will take several decades for the law β = s/g to become true. Now we can understand why it took so much time for the shocks of 1914–1945 to fade away, and why it is so important to take a very long historical view when studying these questions. At the individual level, fortunes are sometimes amassed very quickly, but at the country level, the movement of the capital / income ratio described by the law β = s/g is a long-run phenomenon.
