Ask most people what causes a recession, and you'll get some version of the same story. An economy overheats, excess builds up, and a crash arrives to clean the system out. It's a tidy narrative of boom, bust, and lesson learned.

Tyler Goodspeed, Chief Economist at ExxonMobil and a double-PhD economic historian from Harvard and Cambridge, says that story is largely fiction. His new book, Recession: The Real Reasons Economies Shrink and What to Do About It, examines nearly four centuries of downturns across the US and UK. Almost none of them, he finds, fit the boom-bust template. Instead, he argues, recessions are caused by sudden, often unrelated shocks. These range from energy price spikes and wars to pandemics and even 18th-century piracy.

Here are five of his most counterintuitive findings, in his own words.

1. Boom and bust is the wrong metaphor for recessions.

The most persistent myth Goodspeed set out to test was that expansions carry the seeds of their own destruction, that a boom inevitably invites a bust. His research found the opposite. "There is simply no information in the height, the speed, the duration, or the composition of an economic expansion that can explain anything in terms of the probability, the depth, the speed, the duration, or composition of the subsequent recession." Borrowing a phrase from former Fed chair Ben Bernanke, he puts it bluntly. "Economic expansions don't die of old age or infirmity... they're murdered."

2. The 2008 financial crisis was actually an energy story.

The standard account of 2008 blames reckless mortgage lending and asleep-at-the-wheel regulators. Goodspeed points to energy prices as the real culprit, hiding in plain sight. "The inflation-adjusted price of a barrel of oil, or energy overall, was never more expensive in the past century than in June 2008." That spike pushed the average American household's annual energy spending to a record $8,500, $2,000 more than just a few years earlier. Food inflation climbed above 6%, and mortgage costs rose as adjustable rates reset. Roughly half of US households had no savings after taxes, and food and energy bills weren't easy to cut. "Something had to give." What gave, he says, was mortgage payments.

3. The "dot-com recession" of 2001 wasn't mainly about tech.

Tech stocks crashing is the story everyone remembers about 2001. Goodspeed's data tells a more complicated story. Falling tech valuations were "just one of at least four shocks impacting the US economy" that year, and, by his estimate, "quantitatively it was the least important shock." Natural gas prices spiked that year too, helping sink Enron, and new trade terms with China hit US manufacturing hiring hard. But the biggest factor by far was the September 11th attacks. As Goodspeed puts it, "Without 9/11, there wouldn't have been a recession in 2001."

4. One of America's longest recessions was caused by pirates.

Long before Wall Street existed, Goodspeed found a nearly three-year, depression-level recession in the American colonies from 1717 to 1720, tied for one of the longest in US history. The cause, according to contemporary records, was "unambiguously... pirates." Following the War of the Spanish Succession, large numbers of newly unemployed privateers, including Blackbeard and Calico Jack, turned to blockading ports and disrupting Atlantic trade routes. Goodspeed sees a broader, still-relevant principle at work here. Economic damage often comes down to disruption at a handful of critical shipping chokepoints, he says, a dynamic worth remembering "in the context of Tehran having recently closed the Strait of Hormuz."

5. Nobody can predict a recession, including the people whose job it is to try.

Perhaps Goodspeed's most humbling conclusion is that recessions are fundamentally unforecastable, not because economists haven't built good enough models, but because of a basic logical trap. "If you knew that there was going to be a recession tomorrow, then as a depositor you would withdraw your deposits today... you would get the recession today rather than tomorrow." That unpredictability, he argues, is exactly why expansions behave so differently. Once a shock passes, economies tend to snap back toward their long-run trend. Deeper downturns are typically followed by sharper, faster recoveries.

What about the AI bubble everyone's debating?

Goodspeed is skeptical of confident bubble-calling in general. Looking at past transformative technologies (canals, railroads, fiber optic cables), he notes "there's simply no instance of a contraction in [real physical infrastructure] from a peak to which the economy did not subsequently return." His caution is that people often correctly spot a price peak, then wrongly assume it must cause a recession, when in reality "a lot of these peaks are the casualty of recessionary shocks elsewhere in the economy rather than a cause thereof."

His practical takeaway for ordinary investors isn't exotic (he's also careful to note he isn't a certified financial advisor). Don't try to time markets you can't predict. Keep a diversified portfolio suited to your age and risk tolerance. And hold six to twelve months of liquid savings in reserve, since a shock, when it does arrive, rarely announces itself in advance.