You were any normal Pokémon Trainer who just got everything that you spent a lot of time with in Kanto. You got all gym badges and got every single Pokémon's entries on Your Pokédex except for one, Mewtwo. You went to the Cerulean Cave to go and find Mewtwo in person and catch them. You have a master ball with you that'll catch them without struggle. When you eventually find Mewtwo, they were just standing there doing nothing, as if they were waiting for something. When you came up close to their face, they don't notice you. They couldn't seem to see you right on front of them.