History is a good place to look for answers. Five devastating slumps—starting with America’s first crash, in 1792, and ending with the world’s biggest, in 1929—highlight two big trends in financial evolution. The first is that institutions that enhance people’s economic lives, such as central banks, deposit insurance and stock exchanges, are not the products of careful design in calm times, but are cobbled together at the bottom of financial cliffs. Often what starts out as a post-crisis sticking plaster becomes a permanent feature of the system. If history is any guide, decisions taken now will reverberate for decades.