Impossible

Real does not exist in my book. One person could witness an event, while the other could witness the same event in a different dimension. If a person is to look at a triangle from the bottom straight on he will see one way. If another being is to look at it from the top he is to see two ways. Which one was real and which was an illusion; who believes who? How many sides are there, how many dimensions are there? What is real?