Bruce Willis has so much faith in writer/director M. Night Shyamalan (“The Sixth Sense”) that the star agreed to be in Shyamalan’s new supernatural thriller “Unbreakable” before he even read a word. “There was no script when I said yes,” Willis, 45, told PEOPLE at last night’s “Unbreakable” premiere party at the new Planet Hollywood in Times Square. “It was just an idea. He wouldn’t tell me anything, he wouldn’t tell anybody. He just said, ‘I have an idea for a script that I want to write for you.’ I said, ‘I’m in.’ ” For his part, Shyamalan admitted that he definitely wanted to keep the plot twists under wraps. (Willis plays the only survivor of a train wreck.) As the filmmaker told PEOPLE, “After I wrote ‘Sixth Sense,’ I told Bruce, ‘I got an idea. I can’t tell you what it is, but if you’re in, you’re in.’ He said, ‘I’m in.'” But why all the secrecy? “I don’t like to sell (actors on a project) and I don’t want to hear their reaction.” Shyamalan added that this strategy also worked for Willis’s “Unbreakable” costar, Samuel L. Jackson.