In case it hasn’t been drilled into your head, the highly-hyped film “The Dark Knight” opens today. Thanks to the successful resurrection of the franchise with 2005’s “Batman Begins” and Heath Ledger’s posthumous performance as the Joker, the film will undoubtedly rake in big box office bucks.

Based on the pre-screening I saw earlier this week, the combination of the film’s imminent success and an ending that screams sequel makes a third installment of the franchise inevitable — and that, my friends, scares the bejesus out of me.

But why should it? After all, sequels have proven to be something that most people want.

Take last year’s summer movie season, which was all about the “threequel.” “Spider-Man 3” had the biggest opening weekend of all time with $148 million. “Pirates of the Caribbean 3: At World’s End” and “Shrek the Third” also were third releases in their respective franchises and both had $100 million-plus opening weekends.

Even before that, the third movie in a series was prosperous, like 2006’s “X-Men: The Last Stand,” which set a Memorial Day box office record with almost $123 million over a four-day span.

So why am I concerned about the thought of a third Batman movie? Because it has almost always been proven that the third movie is when a film franchise jumps the shark. This is when quality storytelling and filmmaking usually go out the window in favor of a bigger, harder, faster, stronger follow-up. In “X-Men: The Last Stand,” the story was convoluted by too many mutants with too many powers. “Spider-Man 3” had a key villain turn good and a ridiculously over-the-top final battle involving a high rise and a giant sand dude. “Pirates 3” had Orlando Bloom and Keira Knightly’s characters get married in the middle of a sword fight on a ship slowly sinking into a giant whirlpool. Need I say more.

The franchise of the caped crusader already has suffered the fate of three. Tim Burton’s first two Batman films were good, maybe even comic book classics. But then came 1995’s “Batman Forever,” which swapped Michael Keaton for Val Kilmer, Burton for director Joel Schumacher, darkness for camp and led to the unforgivable sins of 1997’s “Batman and Robin,” which cast “Governator” Arnold Schwarzenegger as a villain and put yet another actor, George Clooney, in a batsuit with nipples. NIPPLES!?!

But a third movie isn’t always the downfall. Certain films, like the “Harry Potter” series, have maintained quality and a large audience, but most of that comes from the popularity of the books. Horror movies can go far beyond the third installment due to the genre’s fans and its nature to shock. Still, most people would agree that “Friday the 13th Part VIII: Jason Takes Manhattan” sucked big time. And let’s not forget the “Rocky” movies. “Rocky III” had the Italian stallion clobbering an opponent played by none other than Mr. T only to follow with 1985’s “Rocky IV,” where the Philly fighter took on a Soviet giant and somehow managed to produce temporary peace during the Cold War at the end of a 15-round bout (although I do admit, I kind of like that one).

Depending on the material, changes in casting, writers or directors, a third movie in a series has a questionable fate. But in the future, when I’m in the theater and see that first teaser trailer for a third Batman, I will be crossing my fingers, hoping that a studio’s desire to cash in doesn’t cause the quality of “The Dark Knight,” or any other good series, to take that dark turn.