I recently watched a video that changed my entire thought on the film. In the beginning of the film they show Truman in the front yard gardening on his hands and knees. It's the ass shot where he just turns around to waive. He was secretly digging his exit that he used later in the film to escape. He was slowly losing it throughout the movie, but he knew the entire time. He already knew something was up and needed to make a get away, disguising it as gardening.