The new all-time high set by the Dow Jones Industrial Average on Tuesday was truly remarkable. How on earth did it take it that long?

After it last reached a high, on January 14 2000, the US suffered a very brief recession and then carried on growing as before. Corporate America did far better than the country as a whole, with companies cleaning their balance sheets, making cuts and taking advantage of capital expenditure investments made during the late 1990s. That earnings boom has continued unabated now for 14 successive quarters.