The most common plot of economic history is the role of surprises. The reason surprises occur is not because our models are wrong or our intelligence is low. It’s because the odds that Adolf Hitler’s parents argued on the evening nine months before he was born were the same as them conceiving a child. Technology is hard to predict because Bill Gates may have died from polio if Jonas Salk got cranky and gave up on his quest to find a vaccine. The reason we couldn’t predict the student loan growth is because an airport security guard may have confiscated a hijacker’s knife on 9/11. That’s all
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