Readers of my stuff will note that, like columnist Gail Collins on the subject of Mitt Romney's dog-on-the-roof, I never pass up an opportunity to point out that World War II cured the Great Depression; and that today we need massive social investment to cure slumping demand. Today, that needed investment, rather than going to war, should go to renewable energy, mitigation of the climate damage already done, and other strategies to allow decent living standards at a much lower toll on the planet. The current low interest rates allow government to borrow serious sums to finance these social investments. What's depressing is that the mainstream debates are over here, and the solutions are over there. While we drag the policies that we need regarding climate change onto center stage, let's at least not make matters worse by raising interest rates.
You can parse the stories about how the bank's risk-management people loaded up on risk, or digest the accounts of how JPMorgan's financial wizards engineered mind-bendingly complex means of limiting their vulnerability to troubles in Europe. But the simplest answer is the most pertinent: It's extraordinarily complicated.