In his book "The Perfect Storm", Sebastian Junger described an event "that may happen only once in a century -- so rare a combination of factors that it could not possibly have been worse."

You're not going to believe it, but this happened to the economy almost 48,000 times in the last month.

I'm not kidding. A Google search shows that at least 48,000 perfect storms have hit the economy since late July. Here's a sampling:

And that's just the economy. A perfect storm also struck Saskatoon's public transit system, a college football game in North Dakota, and a Texas mosquitos, while Justin Bieber's dating life created "a perfect storm of juicy drama."

This is all ridiculous, of course. "Some stuff happened" should replace 99.9% of references to the phrase "perfect storm."

Calling stuff that happens all the time a "perfect storm" isn't just innocent hyperbole. It's dangerous because it makes us discount the danger of an actual perfect storm. If you think stocks and gold losing value at the same time is a perfect economic storm, you will completely lose your mind when Lehman Brothers and AIG collapse in the same week.

According to investor William Bernstein, there are two types of investing risk.

One is "shallow risk," which is a temporary drop in an asset's price. This is normal volatility. "Volatility is the chance that a properly diversified equity portfolio will decline substantially below an investor's cost temporarily, then subsequently recover, then rise to new heights," investor Nicholas Murray told me last month. "This pattern has eventuated every single time throughout history. The average recovery time of all bear markets since 1926 -- with reinvested dividends but also counting inflation -- is about 40 months."

Shallow risk should be looked at as little more than an annoyance. Almost everything the media calls a perfect storm is really just standard shallow risk.

Another type of risk is what Bernstein calls deep risk. Deep risk will legitimately ruin your life. It's when you lose lots of money and have no reasonable chance of ever making it back. 

According to Bernstein, four things cause deep risk: inflation, deflation, confiscation, and devastation.

Germany faced hyperinflation in the 1920s, deflation in the 1930s, and confiscation and devastation in the 1940s. That's deep risk, and a true perfect storm – something that might happen once a century, and a combination of factors that could not possibly have been worse.

"Deep risk," Bernstein writes, is something you "cannot avoid no matter how disciplined and prudent you are." He says it's "a hall-of-mirrors world in which the bedrock principles of finance distort and even invert."

The reason actual perfect storms are so dangerous is because they're so rare. The rarer something is, the less we prepare for it, and the less we prepare for it, the more devastating it is when it arrives. "Risk," financial adviser Carl Richards writes, "is what's left over when you think you've thought of everything." That doesn't happen 48,000 times per month.

Check back every Tuesday and Friday for Morgan Housel's columns.

Contact Morgan Housel at mhousel@fool.com. The Motley Fool has a disclosure policy.