Netflix's "Jessica Jones" and Amazon.com's "The Man in the High Castle" debuted on the same day last month and are battling it out to be the most popular TV series of 2015.
The Internet companies that produced the shows are in a simultaneous battle to be the best-performing large-cap U.S. stock of the year.
Netflix has surged nearly 160 percent this year, and Amazon has jumped 115 percent, the only two members of the S&P 500 to double in value. The index itself has hardly budged, rising 0.2 percent, as of Tuesday's close.
"They're great companies but very richly valued," said Michael Cuggino, president and portfolio manager of the Permanent Portfolio Family of Funds in San Francisco. "There's no question that investors who haven't held those two names have been punished by not owning them."