Rolling Stone's cover interview with David Letterman hits stands on Friday. Mark Seliger Viral videos helped to kill the late-night star.

As the late-night antics of Jimmy Fallon and Jimmy Kimmel went viral, David Letterman identified one of many reasons it was time to retire from CBS's "Late Show."

The lack of ability to create viral videos is "a weakness of the show," Letterman told Rolling Stone as part of a wide-ranging interview set to hit newsstands on Friday.

"I hear about things going viral and I think, 'How do you do that?'" the 68-year-old told the magazine. "I think I'm the blockage in the plumbing."

Fallon and Kimmel have indeed served up many segments that have proved to be successful draws for the YouTube generation, such as Fallon's "Lip Sync Battle," which is now a hit Spike TV show, and Kimmel's "Mean Tweets" and infamous failed twerk video prank.

Despite the tough competition in late night, Letterman has some glowing praise for his colleagues. He calls Fallon's style "bright and colorful" and says Kimmel is "friendly" and "very sweet."

The longtime late-night host has had his own success with innovative sketches. We've all probably clicked on a video of Letterman's "Stupid Pet Tricks" and "Top Ten Lists," among other great segments, but he's probably right about coming just shy of the variety-show-like format of late-night programs nowadays.

"If you look around at the other people doing it and look at me, it's almost like a pair of shoes you haven't worn in a hundred years," he said. "'Gee, I think we can probably get rid of these.' I still enjoy what I'm doing, but I think what I'm doing is not what you want at 11:30 anymore."

On May 20, Letterman will say farewell to his show after 22 years at CBS, with the help of a cadre of big stars, including Tom Hanks, George Clooney, Jerry Seinfeld, Oprah Winfrey, and one of the Obamas. Even former nemesis Jay Leno has been invited, according to the magazine, though he has yet to say whether he will make an appearance.

Comedy Central's former "Colbert Report" host Stephen Colbert will take over "Late Show" on September 8.