"When I sat down to write the sequels, I knew there were going to be three at the time, and eventually it turned into four," Cameron said.

He added: "I put together a group of writers and said, 'I don't want to hear anybody's new ideas or anyone's pitches until we have spent some time figuring out what worked on the first film, what connected, and why it worked."

The writers apparently still didn't get it at first, and Cameron had to threaten that he would let them go, which eventually worked.

"They kept wanting to talk about the new stories. I said, 'We aren't doing that yet.' Eventually, I had to threaten to fire them all because they were doing what writers do, which is to try and create new stories. I said, 'We need to understand what the connection was and protect it, protect that ember and that flame'," he said.