If summer 2011 proved anything at the movies, it was the enduring wisdom of screenwriter William Goldman’s axiom about Hollywood: Nobody knows anything.

Some of the movie business’s most cherished assumptions have been summarily smashed to bits since Memorial Day, which mostly bodes well for audiences. An industry that caters almost exclusively to teenage boys is finally poised to take other audiences seriously. (Please, God, let this mean fewer comic-book movies.)

Herewith, some lessons learned:

3-D is over. Unless you’re Werner Herzog (see below).

For the past few years, Hollywood, especially DreamWorks SKG co-chief Jeffrey Katzenberg, has been chanting the same “Music Man”-like refrain: “3-D, it’s the future!” Audiences finally seem to be seeing through the hype, declining to fork over an extra $5 for a muddier, murkier version of a below-par movie, whether it’s “Glee: The 3D Concert Movie,” “Conan the Barbarian” or the latest “Spy Kids.” (The “Harry Potter,” “Transformers” and “Pirates of the Caribbean” movies did especially well overseas, where 3-D is still a bankable novelty.) What the studios learned, says INDIEwire box office analyst Peter Knegt, is that “3-D is not the end-all groundbreaking thing that’ s going to change everything.” Upshot: Look for fewer 3-D movies, at lower prices and with higher production values.

Girls — no, make that moms — rule. With such films as “Bridesmaids” and “The Help” becoming bona fide sleeper hits this summer, Y-chromosome-obsessed moguls can no longer deny the fact that women are a lucrative market (a lesson they began learning with the past successes of “Sex and the City,” “Mamma Mia!” and the “Twilight” movies). Teenagers, meanwhile, failed to show up at theaters as reliably as they have in the past, relegating such “sure things” as “Green Lantern,” “Cowboys & Aliens” and “Fright Night” to the ash heap of “Wha’ happened?!” Said one studio executive to The Hollywood Reporter, “Cracking the nut of why young people are missing is a big problem.” Upshot: Look for more movies aimed at women and their daughters.

It’s the economy, stupid. Again. Analyst Phil Contrino may have cracked the aforementioned nut. The editor of Boxoffice.com calls the economic downturn the “elephant in the room” when it comes to teens’ absence from the multiplex. “The fact that the economy is bad for adults means it’s even worse for teenagers,” he says, noting a trend that started last winter, when such adult-oriented dramas as “True Grit,” “Black Swan,” “The Fighter” and “The King’s Speech” outpaced expectations at the box office. “It happened again this summer with ‘Bridesmaids,’ ‘The Hangover Part II’ and ‘Midnight in Paris,’ ” he says, all of which were geared to the 25-and-up demographic. Upshot: Look for more movies aimed at grown-ups, and not just at Christmastime.

That Woody Allen kid just might make it! The 75-year-old Allen’s whimsical romantic comedy “Midnight in Paris” made more than $50 million this summer. (Cineastes can quibble over whether, adjusted for inflation, that figure makes “Midnight” more successful than such Allen classics as “Manhattan” or “Annie Hall”). Herzog’s trippy documentary “Cave of Forgotten Dreams” has made more than $5 million, the most successful film of his career (3-D receipts admittedly account for the lion’s share of that take, proving that in the hands of artists, it can be a valuable expressive tool). Even Terrence Malick did pretty well with the maddeningly opaque “The Tree of Life” ($13 million and counting). While comic-book superheroes floundered, these success stories proved that there’s still room in theaters for strong, singular, challenging visions. Upshot: Look for the survival of auteurs, their eulogizers to the contrary.

Ryan, your career needs a rethink. Not you, Mr. Gosling. “Crazy, Stupid, Love” was supposed to be a sleeper hit. It turned out to be a bland, tonally challenged contrivance — but one featuring an utterly winning performance by red-hot Ryan Gosling. The 30-year-old actor sizzled opposite Emma Stone, proving in no uncertain terms that he is a Movie Star, and shows promise of doing so again in “Drive” and “The Ides of March” this fall. Ryan Reynolds, on the other hand, starred in two of what the Hollywood Reporter deemed the summer’s biggest duds: “Green Lantern” and “The Change-Up.” Upshot: Look for Reynolds in more romantic comedies a la “The Proposal” with Sandra Bullock; look for Gosling holding an Oscar very soon.

No one ever went broke working blue. Remember when “The Hangover” surprised everyone by becoming an under-the-radar hit? It took its so-so sequel — and such raunchy cousins as “Horrible Bosses,” “Bad Teacher” and “Bridesmaids” — to prove that, when it comes to rank vulgarity, exploitative sexuality and sophomoric sight gags, the rung can be ever lowered. Upshot: Look for more R-rated comedies and squeamish film critics’ offended moral sensibilities.

No one ever went broke being blue. First came “Avatar” and its heroic indigo-hued indigenous protagonists. Now comes “The Smurfs,” the summer’s most irritating, inexplicable hit that critics hated and no one seems to have seen but that has grossed a gobsmacking $400 million worldwide. “For whatever reason, it worked, and I don’t understand why,” says Knegt, who adds that nostalgia and a dearth of family fare late in the summer probably had something to do with it. Four hundred million dollars, people. It’s on you. Upshot: “The Smurfs 2,” “The Smurfs 3,” “The Smurfs 4”. . .