The is up a bit more than 6 percent in 2014, and while that isn't breathtaking, the gains have been consistent enough to bring the index to 22 all-time closing highs. What may be less widely known is the role that earnings expectations appear to have played in the gains.
In order to create what's known as a "blended growth rate" for earnings in the first half of the year, FactSet senior earnings analyst John Butters takes the earnings that companies actually reported for the first quarter and combines that with bottom-up analyst expectations about the earnings companies will report in the second quarter. For the first half of 2014, the S&P's blended earnings growth rate is 3.7 percent. When he combines the earnings estimates for the third and fourth quarters, he finds that the overall forecast for earnings growth in the second half is 9.9 percent.
"One possible reason for the rise in the value of the market is the expectation for much higher earnings growth in the index in the second half of 2014," Butters concludes.
This logic certainly comports with the thinking of bullish strategist Jonathan Golub. The chief U.S. market strategist at RBC Capital Markets, Golub determines that "the change in NTM [next 12 month] EPS expectations has contributed 4.6 percent of the S&P 500's 6.2 percent return."
This fact gives Golub confidence that the market will continue higher, eventually reaching his 2,075 target for the end of the year.
"Importantly, the market's return since January has largely been driven by corporate results as opposed to multiple expansion, a healthy sign in our view," he wrote in a Monday note.
Of course, the flip side is that if companies don't actually grow earnings at the blistering 10 percent pace expected in the second half, equities could start to run into some serious trouble.
Read More Mario Gabelli reveals second-half playbook
So where might expectations be the most overheated?
Look to the financials. Using FactSet's blended estimate, earnings in that sector are seen as down 2.7 percent in the first half. But in the back half of the year, analysts are looking for earnings growth of 15.5 percent, with JPMorgan expected to be the largest contributor.
—By CNBC's Alex Rosenberg
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