1. John Francis Daley (Sam Weir) was the only cast member playing a character his or her age.

Daley was 14 in real life and on TV. Linda Cardellini, then 24, played his 16-year-old sister Lindsay. Samm Levine (Neal Schweiber), Martin Starr (Bill Haverchuck), and Seth Rogen (Ken Miller) were all 17. Jason Segel (Nick Andopolis) was 19. Busy Phillips (Kim Kelly) and James Franco (Daniel Desario) were 20 and 21, respectively.

2. The camera crew was under strict orders to make scenes look drab.

Freaks and Geeks takes place in fictional Chippewa, Michigan, a suburb of Detroit. The crew used green and gray-tinted lights to achieve so-called Midwestern colors on the show's set in California. They also avoided shooting outdoors whenever possible.

3. Most of the show's budget was spent on music

The show's 18 episodes featured snippets of more than 120 songs, including Joan Jett's "Bad Reputation" in the opening credits. It set the tone for the show, but it wasn't cheap. Clearing songs by Van Halen, KISS, and The Who—just to name a few—required a lot of paperwork and ate up much of the show's budget . It also later delayed the DVD release. Fox removed most of the music when it picked up Freaks and Geeks re-runs to avoid paying extra fees.

One song that got away: Neil Young's "Only Love Can Break Your Heart." When producers couldn't get the licensing rights for episode 15, they replaced it with Dean Martin's "You're Nobody 'Til Somebody Loves You."

4. Executive producer Judd Apatow might not have worked on Freaks and Geeks at all.

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He took the job after Fox didn't pick up his pilot Sick in the Head, a sitcom about a rookie psychiatrist's first days working the psych ward. David Krumholtz was cast as the lead, and a pre-SNL Amy Poehler played one of his suicidal patients.

5. Creator Paul Feig started his career as an actor.

He and Apatow met on the L.A. comedy circuit in the mid-1980s and worked together on the set of the 1995 film comedy Heavy Weights, which Apatow wrote with Steven Brill. TGIF fans might remember Feig as Eugene Pool, Sabrina's biology teacher on the first season of ABC-TV's Sabrina, the Teenage Witch.

6. Feig's inspiration for the show was his own life—and a 14-part West German TV miniseries called Berlin Alexanderplatz.

The 1980 miniseries is also about an outcast—a man trying to make a new life for himself after accidentally killing his lover and serving four years in prison. It's based on the 1929 novel by Alfred Döblin.

7. Judd Apatow hired 24-year-old Jake Kasdan to direct the pilot without ever seeing his work.

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Kasdan had written and directed just one movie, the detective flick Zero Effect. Apatow was aware of his work because the two men shared an agent. He hired Kasdan on the agent's advice and watched the movie the next day. Fortunately, things worked out.

Kasdan has since found steady work as an executive producer on New Girl and directing films like Orange County and Bad Teacher.

8. Everything on the show actually happened to Feig or one of the show's writers.

To jump-start the writing process, Feig had writers fill out questionnaires about their own experiences in high school. Questions included: "What was the best thing that happened to you in high school? What’s the most humiliating thing that happened to you in high school? What’s the first sexual thing you ever did?” The answers were used to create the show.

9. Well, except for episode 17, "The Little Things." That was inspired by The Howard Stern Show.

Spoiler alert! Neither Feig nor any of the writers had ever dated someone with ambiguous genitalia like Ken (Seth Rogen) did in episode 17. Instead, Judd Apatow got the idea while listening to Howard Stern. At this point, everyone was pretty sure Freaks and Geeks wouldn't be renewed. Apatow later told Vanity Fair, "In a way, it was a 'F**** you' to NBC, like 'Now we’re going to get really ambitious and aggressive with storylines that you would never approve if the show had a chance of surviving.'"

10. Timing—in this case, bad timing—was everything.

Freaks and Geeks premiered on September 25, 1999 in one of NBC's deadliest time slots—Saturdays at 8 p.m. To make things worse, it wasn't aired continuously. The show was taken off air during the World Series in October, and later put in a new time slot against ABC's then-red-hot Who Want to Be a Millionaire. Reviews were great, but Freaks and Geeks couldn't keep an audience.

The producers created a website for the show, hoping that it would keep fans engaged and aware of upcoming episodes. The bigwigs at NBC refused to share the URL on ads, because they didn't want to promote Internet use over watching TV.

11. The show's finale was written and filmed in the middle of the season.

NBC originally ordered 13 episodes of Freaks and Geeks. With the threat of cancellation looming, Feig wrote and directed the finale, "Discos and Dragons," so that the show could end on a strong note. Then NBC ordered five more episodes, so that pushed the finale forward a few weeks. Three of these episodes never aired until Fox syndicated the show.

12. Freaks and Geeks was a critical darling, but won only one Emmy, for Outstanding Casting in a Comedy Series.

Casting is one of the Creative Arts Emmy categories awarded in a ceremony held separately from all the acting awards. Paul Feig was also nominated for Outstanding Writing for a Comedy Series (both in 2000 for the series pilot and in 2001 for the finale), but he came up short both times.

13. Speaking of casting, here are a few ways the show could have been very different.

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Jesse Eisenberg (later of The Social Network) was nearly cast as Sam Weir. Busy Phillips (Kim Kelly) originally auditioned for the role of Lindsay Weir. A few other almosts: Lizzy Caplan of Masters of Sex auditioned for the roles of Kim Kelly and Lindsay; Lauren Ambrose of Six Feet Under also auditioned for Lindsay; and Shia LaBeouf tried out for the part of Neal Schweiber.

NBC pressured the show's producers to stunt-cast celebrities in small roles to attract viewers. Britney Spears was one suggestion. They refused.

14. Samm Levine's (Neal Schweiber) William Shatner impersonation helped him get the part.

But not because it was good. Judd Apatow thought it was hilariously bad—exactly like something a geek would do.

15. The cast was encouraged to pursue their own writing.

During some downtime on-set, Feig and Apatow showed James Franco how they brainstormed and wrote scenes. Jason Segel and Seth Rogen improvised new jokes when they rehearsed on weekends. Instead of taking GED correspondence courses while filming, Rogen started writing his first screenplay, Superbad.

16. The cast and crew stuck with the theme for the series wrap party.

Instead of your typical Hollywood soiree, the party's theme was a high school prom in 1980. Everyone wore late '70s formal wear, except for Busy Phillips, who wore the dress she wore to her real junior prom. Paul Feig even had special class rings made for himself and Judd Apatow.

17. Paul Feig brainstormed some of the story lines for season two.

What might we have seen if Freaks and Geeks hadn't been cancelled? Feig imagined something bad happening to Lindsay while she was following The Grateful Dead, ultimately destroying her parents' trust. Sam was going to find his voice as a drama geek, while Neal joined the school chorus. (Who's geekier now?) Bill would become a late-blooming jock under the care of Coach Fredricks, who might have become his stepfather.

The freaks had more serious plot twists ahead. Daniel would end up in jail, Nick would probably join the Army after graduation, and Ken's fate was never quite clear.

There's still some hope that Freaks and Geeks might come back someday, albeit with a new cast. Feig has said he'd love to see a musical adaptation.

18. Feig later wrote two memoirs.

The book Kick Me: Adventures in Adolescence, published in 2002, revisits the teen angst that made Freaks and Geeks so funny and relatable. Three years later, Feig recalled his painfully chaste early adulthood in Superstud: Or How I Became a 24-Year-Old Virgin.

19. After Freaks and Geeks, Feig and Apatow went their separate ways in the world of TV.

Apatow became the executive producer and creator of the Fox sitcom Undeclared, which was also cancelled after one season. He hired Seth Rogen as a staff writer and put other Freaks and Geeks cast members in recurring roles. In 2001, Apatow wrote another pilot about struggling actors for Fox, called North Hollywood. Seth Rogen, Jason Segel, and Kevin Hart all had roles. In a case of life imitating art, the show wasn't picked up. Soon after, he became a Hollywood heavyweight with box-office hits like The 40-Year-Old Virgin and Knocked Up.

Feig directed one episode of Undeclared. After that, he worked as the co-executive producer of The Office and Nurse Jackie and directed multiple episodes of Arrested Development and Weeds.

20. Feig and Apatow didn't team up again until Bridesmaids in 2011.

It became the highest grossing R-rated female comedy ever, not to mention the highest grossing film of Apatow's very successful career. Now the two are said to be working on another romantic comedy to be written and directed by Feig.