Shutter Island
In the last act of Shutter Island, former U.S. Marshal Teddy (Leonardo DiCaprio) learns that his entire stay at Shutter Island was an elaborate roleplay orchestrated by his doctors in order to make him remember who he really is—Andrew Laeddis, a man who murdered his psychotic wife after she drowned their three children. The movie concludes with Laeddis reverting to his old persona, leaving doctors with no choice but to lobotomized him. However, Laeddis' final line led audiences to believe that he simply refused to live with the pain of his past: "Which would be worse; to live as a monster or to die as a good man?"
Black Swan
Natalie Portman and Mila Kunis play rival ballet dancers with a strange connection that is only revealed toward the end of the film. After Nina (Portman) stabs Lily (Kunis), she steps on stage to dance in Swan Lake—only to realize that Lily was a stress-induced hallucination, meaning Nina has actually stabbed herself. Although Nina's fate remains a mystery, she certainly gave the performance of a lifetime.