“There’s only five people in the world who know exactly what being on Friends was like, other than me,” Matt LeBlanc tells Warren Littlefield, the former president of NBC Entertainment, whose book Top of the Rock: Inside the Rise and Fall of Must See TV is excerpted in the May issue of Vanity Fair. “There’s five of them. David, Matthew, Lisa, Courteney, and Jen. That’s it.” Littlefield talks to cast members, creators, writers, and producers about what made the decade-long show so special. “Lisa Kudrow said it best,” LeBlanc recalls. “She said that she worked harder on these relationships than she did on her marriage.”

Co-creator Marta Kauffman said they knew they had something special the first time the cast all came together: “The first day we went to a run-through, and the six of them were together for the first time, onstage in the coffee shop, I remember the atmosphere being electric. A chill ran down my spine.”

Kudrow explains that the cast, led by Courteney, decided from the very beginning that they had each other’s backs: “Courteney Cox was the best known of all of us, and she had done a guest star on Seinfeld. She said, ‘Listen, I just did a Seinfeld, and they all help each other. They say, “Try this,” and “This would be funny.” And she said, ‘You guys, feel free to tell me. If I could do anything funnier, I want to do it.’ There’s a code with actors. Actors don’t give each other notes under any circumstances. So she was giving us permission to give her notes, and we all agreed that that would be great. Why not? And she also said, ‘Listen, you know, we all need to make this thing great.’ She just set the stage with: ‘I know I’m the one who’s been on TV, but this is all of us.’ She was the one who set that tone and made it a real group that way. And I thought that was a real turning point.”

“Six of One was the name of the show during the pilot,” Karey Burke, former prime-time executive at NBC, explains. “Then Kauffman and Crane came back with Friends, which we thought was such a snore. Some people thought the show was too Gen X, way too narrow.”

“It was a fascinating casting experience,” says Marta Kauffman on casting the pilot. “We saw a countless number of actors.… One of the first actors on our list was Matthew Perry to play Chandler, but he was doing a show called LAX 2194 [a Fox pilot about baggage handlers in the year 2194], so he wasn’t available. We brought other people in.” Kauffman’s writing partner, David Crane, goes on to explain, “We brought everybody in. We were so sure that Chandler would be the easiest part to cast. It’s got the most joke jokes. It’s sarcastic and kind of quippy, but no one could do it. No one.” The closest they got was Craig Bierko, who, Kauffman explains, they later found out had been coached by Perry. Bierko read the script and passed. “Thank God! There was something Snidely Whiplash about Craig Bierko,” says Littlefield. “He seemed to have a lot of anger underneath, more of a guy you love to hate. The attractive leading man who you love and can do comedy is very rare.” Eventually Matthew Perry was released from his Fox pilot.

“We originally offered Rachel to Courteney Cox,” says Kauffman, “but she said she wanted to do Monica, not Rachel.” Kauffman and Crane initially had a different vision for Monica. “When we originally wrote the role, we had Janeane Garofalo’s voice in our head,” explains Crane. “Darker and edgier and snarkier, and Courteney brought a whole bunch of other colors to it. We decided that, week after week, that would be a lovelier place to go to.” Cox did have competition, though, explains former head of casting at NBC, Lori Openden: “Nancy McKeon, from The Facts of Life, also read for Courteney’s part. She gave a terrific performance. Warren let Marta and David make the call. They went off for a walk and came back and said Courteney.”

Related: Vintage set and cast photos from the heyday of Friends on NBC, starring Jennifer Aniston, Courteney Cox, Lisa Kudrow, Matt LeBlanc, David Schwimmer, and Matthew Perry.