This scene was exquisitely filmed. Truman is alone on a boat out in the middle of beautiful nowhere and the bow of his boat ruptures the backdrop painted as a beautiful sky of a movie set, where the wall between reality and fiction is erected. Initially, Truman doesn't get it, and doesn't understand it, but as his hand goes searching for concrete evidence the look on his face is "I knew it all along," and he did. It just didn't pierce his conscience. He just didn't have a critical mind. He was raised on innocence, reaffirmed by loving, doting parents who wanted to extend their parenting years of a child for as long as they could, so he had no reason to believe that innocense inspired by parental love wasn't the best model.
Then he steps out of the boat alone and begins to investigate, to walk along a plank that is supposed to be the water. He's playing the Jesus walking on water with Truman being his own best savior.
The Truman Show, 1998. There was another great movie that year, 1998, named Enemy of the State, starring Gene Hackman and Will Smith.
