Sorkin created the beloved political drama and served as showrunner for its first four seasons. He departed in 2003 owing to conflicts with Warner Bros TV, and John Wells took over as sole executive producer.
In an interview with Vulture, Sorkin admitted that he could not bring himself to watch the episodes made after his exit, comparing it to "watching somebody make out with [his] girlfriend".
Asked whether he had regrets about not having stayed, Sorkin confirmed: "Yes. Sure."
With regard to the idea - held by many fans of the show - that its quality dropped following his departure, he explained: "I'm unable to [assess the quality of those episodes], and I'll tell you why.
"Less than an hour after the press release went out toward the end of season four [announcing] that Tommy Schlamme, our principal director, and I would be leaving the show, Larry David called me."
Seinfeld co-creator David had left that show before the end of its run, and he advised Sorkin never to watch the show again, saying that it would only make him "miserable" whether it was good or not.
Sorkin explained that he initially shrugged off David's advice, but when he was sent a copy of the fifth-season premiere he couldn't bring himself to watch it.
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"I stuck the tape in, and I did not get even 60 seconds into it before I had to shut it off. Not because it was great, not because it was less than great, but because it was like watching somebody make out with my girlfriend.
"Other than those 60 seconds, which I can't even really recall, I've never seen seasons five through seven.
"I missed it terribly when I left. But it was the right thing to do."
Sorkin's new HBO series The Newsroom, set behind the scenes at a cable news channel, premieres on June 24. Watch a trailer below: