As the market hits record highs, the is also setting another, quieter record. As the final fourth-quarter earnings trickle in, S&P 500 companies have reported record aggregate earnings per share of $28.78.
And since earnings are anticipated to improve from here, the market's forward price-earnings ratio still remains below its 15-year average, despite the record-high prices.
The S&P 500 is currently trading at a forward price-per-earnings ratio of about 15.4, which is above both the five-year average of 13.2 and the 10-year average of 13.8. But over the past 15 years, the market's average P/E ratio is 16.0, according to FactSet.
"With the forward P/E still below the 15-year average and not close to the higher P/E ratios recorded in the early years of this period, one could argue that the index may still be undervalued," John Butters, senior earnings analyst at FactSet, wrote in a recent note.
For 2014, analysts expect to see earning growth of 8.8 percent. Now, it is true that analyst estimates tend to be almost strangely optimistic, especially several months out. But the stock market is still generally thought to be a leading indicator for the direction of the economy. If the actual earnings growth is close to the growth anticipated, then the stock market may not be too expensive at all.
(Read more: Either analysts are wrong, or stocks will go crazy)
"At the end of day, it's really earnings that are the driver of the stock market," Butters told CNBC.com. "Maybe it's other things from time to time, but as you go over a longer and longer time frame, it's really the earnings that matter."
This point is made dramatically by a chart comparing the performance of the stock market with trailing 12-month earnings per share (so, the earnings that were actually reported by S&P 500 companies in the preceding 12 months, rather than the earnings that analysts expect companies to earn in the following 12 months).
The fact that that chart of the S&P 500's earnings, and the chart of the S&P 500, are nearly the same chart speaks to the importance of earnings to the stock market.
Unless earnings severely disappoint in 2014, then, perhaps investors are better off setting the oft-voiced fears about exuberance and complacency aside. At the end of the day, the price that investors are paying for stocks may not be quite as important as what they are actually getting for their money.
—By CNBC's Alex Rosenberg. Follow him on Twitter: @CNBCAlex.
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