What goes up must go down.
Sir Issac Newton, the physicist and mathematician, was talking about the laws of gravity. But he could have been talking about modern economies and markets, which over the past 25 years have been punctuated by "the bubble-and-bust mentality," as President Barack Obama described it.
There was the Russian financial crisis in 1998, which led to the failure of the early hedge fund Long-Term Capital Management and the near failure of Bear Stearns. There was the Argentine economic crisis in 1999, which put that country in bankruptcy. Back in the U.S, there was the dot-com boom and bust in 2000.
And then there was granddaddy of them all: the subprime-led crisis of 2008. That led to the Great Recession, which, in turn, created a global panic and morphed further into a series of crises across Europe. "You never know who's swimming naked until the tide goes out," Warren Buffett famously said.
So have we learned anything from the past 25 years? Or are we sitting on the edge of another crisis?