Film history is littered with the corpses of sequels to your favorite comedies.

That's something that 'Anchorman 2: The Legend Continues' director Adam McKay and star Will Ferrell know and it's probably one of the key reasons why the sequel took nearly a decade to get made. Any sequel runs the risk of tarnishing a legacy of a good movie, but a new chapter in a comedy series often feels like a black hole that sucks the funny out of something that used to crack you up. We see a bad sequel to an action movie and we shrug, disappointed. We see a bad sequel to comedy and it just makes us sad.

But, why is it so difficult? In this sequel and reboot-laden era, we're used to follow-ups being thrown at us left and right. In fact, Hollywood seems to have gotten pretty good at making sequels that surpass the original in every way (especially in the realm of superhero movies), but comedies remain troublesome. Ask a random assortment of people if they enjoy 'The Hangover' and you'll get plenty of affirmatives. Ask the same people if they like 'The Hangover Part II' and you'll get nothing.

Perhaps it's because the usual rules of making a sequel don't (and usually can't) apply to comedies. With a sequel to an action film, you just increase the budget and make everything bigger, enlarging the stakes and providing more spectacle. For example, you add a Batman and Wonder Woman to your 'Man of Steel' follow-up. But, this won't work for a comedy, because higher stakes don't necessarily make a movie funnier. Both 'Hangover' sequels went bigger and crazier without bothering to get funnier. Increasing the sheer number of awful things that happen to your cast of characters isn't a great recipe for comedic success. Comedy is about delivery, not scale.

'The Hangover Part II' was also guilty of another problem that most comedy sequels run into: repetition. Often times, the makers of a successful comedy take a "if it isn't broken, don't fix it" approach to their sequels. If it made people laugh the first time, it'll work again, right? This has led to more than a few comedy sequels that intentionally tread the same ground as their predecessor, hoping to squeeze laughs out of recognition. This is what derails the occasionally amusing (but mostly dull) 'Ghostbusters 2,' which resets its characters to the status quo at the start of the first film and works to build them up again. It's why the 'Austin Powers' films become so painful, as Mike Meyers and his team insisted on callbacks instead of fresh material. It's not necessarily lazy filmmaking, but it's uninspired filmmaking ... and it's filmmaking that thinks the audience are a bunch of morons who will accept the same movie twice.

On occasion, you'll find a comedy sequel that just feels lazy and desperate in every frame, a reunion that feels like it was done out of financial necessity and no one on or behind the camera actually cares. This is evident in 'Ghostbusters 2,' which abandons the creepy, moody look and character-driven comedy of the original and embraces flat, comedy lighting and easy jokes. It's even more painful in 'Men in Black 2,' which throws away the wry, clever world-building of the first entry and replaces it with easy jokes and a lot of Will Smith shouting.

'Caddyshack 2.' 'Be Cool.' 'The Blues Brothers 2000.' 'Evan Almighty.' Is it any wonder that we're nervous as hell about 'Anchorman 2'? Comedy sequels don't have a solid track record as it is, so our excitement for the return of Ron Burgundy has to be tempered by the fact that this is a decade-late sequel starring some guys who, while certainly well-liked, would very much like to have a massive hit on their hands. We'd like to think that if anyone can make a great comedy sequel it would be these guys, but brings us to our final concern and the main reason why continuing a comedy series is so hard.

It's simple: comedy is alchemy. You can't really structure it. You can't really define it. Classic comedies rarely come together by design -- they come together because the right people got in the right room at the same time and the stars aligned. The first 'Anchorman' feels like a miracle. We didn't know that Will Ferrell and Steve Carrell and Paul Rudd and Adam McKay would go on to be some of the most important comedic voices of our time. When McKay was shouting out improv suggestions from behind his camera, he had no idea that we'd be quoting them for nine years. Comedy is magic and it's born out of chaos. Comedy works in the first place because comedy is surprising.

'Anchorman 2' can't be chaos. We know these characters. We have a general idea of what to expect. The cast and crew know that what they're working on is a big deal. These aren't people being funny in a bubble. These are people being funny in a brave attempt to exceed impossible expectations.

And that's probably the best reason why making a comedy sequel is so problematic. Replace surprise with familiarity in a comedy and what do you get? A tired sequel. We want to see a new classic more than anyone in the world. Just forgive us if we keep our excitement a little muted. We've been burned way too many times.

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