My professors in film school were great people, but I can't tell you how many screenwriting how-to manuals they subjected me to during my four years of college, some of which were 500 pages long. Reading those books always begged the question: If these guys know so much about writing great screenplays, why haven't they written any themselves?

Here are the biggest film disasters from self-proclaimed experts of cinema...

"Barbie in the 12 Dancing Princesses" (Robert McKee)

McKee is truly the godfather of screenwriting books as the writer of ubiquitous film school bible "Story: Substance, Structure, Style and the Principles of Screenwriting." In fact, so famed is McKee that he was even portrayed by actor Brian Cox in a key NSFW scene from "Adaptation" (an actual great screenplay).

Which is interesting because the acclaimed script master has never had a single movie of his own make the big screen, only a few television and straight-to-video credits. For example, this lightly regarded animated Barbie movie, of which McKee is credited as "story consultant," not even as the screenwriter.

"Spree" (Syd Field)

After McKee, Field (who died last year) was the second biggest name in screenwriting books, with titles such as "The Screenwriter's Workbook" and "Selling a Screenplay: The Screenwriter's Guide to Hollywood." But he wrote just one feature film himself...and it was a documentary to boot: "Spree," a little-seen 1967 movie about Las Vegas nightlife.

"Stop! Or My Mom Will Shoot" (Blake Snyder)

While McKee and Field were from the old school, Blake Snyder was the new age guru. His "Save the Cat! The Last Book on Screenwriting You'll Ever Need" has become the modern classic on putting cinematic words to the page.

Snyder, who died in 2009, was surely far more successful than McKee and Field, banking millions in spec script sales and even having two scripts hit the big screen. Unfortunately, those were the flop "Blank Check" and the even bigger flop "Stop! Or My Mom Will Shoot," a Sylvester Stallone vehicle that currently has an abysmal 4% "fresh" rating on Rotten Tomatoes.

"Terminal Invasion" (John Jarrell)

On the jacket copy of "Tough Love Screenwriting: The Real Deal From A Twenty-Year Pro," the brash Jarrell boldly proclaims that his book is not another "mass-marketed screenwriting hustle based on shortcuts, gimmicks, getting rich quick, smarmy 'plug in your story' paradigms or the 'what Hollywood wants' approach."

Maybe he should actually learn what Hollywood wants, as his last-produced movie is this 2002 Bruce Campbell picture about aliens disguising themselves as humans to take over a rural airport. The real deal? A mere 33% of moviegoers actually enjoyed it.

"Group Marriage" (Richard Walter)

Walter isn't just another swindler who cashed in on unemployed coffee shop dwellers hoping to turn their dumb ideas into loot. He's actually the head of UCLA's Department of Film and Television, and his students have won Academy Awards for films such as "Milk" and "The Descendants."

Unfortunately for Walter, author of "Essentials of Screenwriting," his one produced screenplay isn't quite as well-regarded as his proteges' work. 1973's "Group Marriage" (extremely NSFW trailer here) is an obscure "romp" about a dozen young Californians who move into a communal home, so they can begin swapping sex partners.

My advice? If you truly want to learn about screenplays, read William Goldman’s books "Adventures in the Screen Trade" and "Which Lie Did I Tell?" Goldman is one of the greatest writers in Hollywood history, having penned such classics as "Butch Cassidy and the Sundance Kid," "All the President's Men," and "The Princess Bride." Unlike the other gurus, his IMDB speaks for itself.