In perhaps the least shocking economic data point to be released this month, American consumers were sharply less confident about the economy in early October than they were in September. Turns out, shutting down the government for 16 days while using the threat of a government debt default to battle over the nation's budget isn't great for peoples' psyche.

The index was down to 71.2, from 80.2. It's interesting that the Conference Board's measure of "present conditions" fell much less than its index of "expectations." In other words, the problem Americans were facing was not so much an actual worsening of their economic situation (surely government employees and many contractors were an exception to that rule) so much as a confidence-jarring hit to their expectations for the future.

So, should we be worried? In 2011, the debt ceiling standoff showed up in the form of weaker retail sales and business investment. But that one included much more volatility in financial markets, in part because Europe was in an intense phase of its own economic crisis at the same time.

And it's worth remembering that measures of confidence are always far more volatile than the actual amount of money Americans spend. This chart, for example, shows the percent change in the University of Michigan consumer sentiment index (in blue) against the percent change in personal consumption expenditures in a given month.

Source: University of Michigan and Bureau of Economic Analysis, via St. Louis Fed's FRED database

Our emotions, in other words, are subject to wilder swings than is our actual behavior when making purchases. And it's not just a difference in volatility. The correlation between the two numbers is startlingly weak: Only 4.5 percent from 1978 through this past spring. In other words, if you know what happened to either consumer sentiment or consumption spending in a given month, it tells you almost nothing about the other.

So there are no guarantees that the plummeting consumer confidence will materialize into worse economic results for October. Still, coming off of a slew of weaker-than-expected data, it's hard to imagine that the wallop that consumer confidence took in October will help matters.