Further exclude third- and fourth-largest contributors Facebook and Netflix, and we're looking at an index that's actually down 5 percent in 2015.
Of course, some stocks always perform better than others. But the narrow leadership of the Nasdaq 100 has become a major topic of conversation on Wall Street.
"The money continues to crowd into the same names. The gap between the FANG stocks and the SPX remains wide," Michael Block, chief strategiest of Rhino Trading Partners, wrote in a Thursday note, referring to an acronym for Facebook, Amazon, Netflix and Google and to the S&P 500 index.
"This will eventually end in tears," Block warned.
Larry McDonald, head of U.S. strategy at Societe Generale, believes that such "crowding" is reflective of general fears about the market on the part of asset managers.
"What you're really seeing is fear," he told CNBC. "Let's say that you have to be invested in stocks, or perhaps in growth stocks specifically. Well, if you're nervous about the market, you're going to pick the biggest, most liquid names possible — your Facebooks, your Googles, your Amazons."
For that reason, McDonald sees the stunning outperformance of a few choice names as an ironic reflection of bearish sentiment that will eventually take the overall market lower.