Dan Scanlon has compared making a Disney-Pixar film to helping an unruly child through its teenage years.
The Monsters University director explained he was pleased with the end product of his upcoming movie but that like "every" Pixar movie it was "horrible" to begin with.
He said: "We threw a ton out, don't get me wrong, but I'm glad it's gone, all of it was a terrible mistake.
"We had a million different versions of the movie and they were all horrible. Every Pixar movie is horrible in the early stages, it goes through an awkward teenage stage and then hopefully it makes it out."
Dan said he felt Pixar had given him plenty of opportunities to make any changes he wanted and had been "very supportive".
He said: "There really wasn't a lot walking away that I feel like we could have done that differently."
Monsters University follows Monsters Inc favourites Mike and Sulley through their university years when they first meet and haven't yet become the best of friends. The film is released in cinemas on July 12.