Then they show him that the whole world has been created by a simulation program. This includes all the details he has seen. Cars, the noise of the city, traffic, skyscrapers, ocean, people, basically everything he sees and experiences are just animated in his brain with a computer program.

     The person that shows him the facts also tells him that he has been living in a virtual life and he imagined everything to be real. And yet the real world at that time is totally different. There is just a collapsed, destroyed world. All the nice modern buildings and cars are just imaginations in his brain.

     He learns that even the history he thought was real was a dream and that he actually lives in a totally different time.

     Another scene from the movie The Matrix. The person in this scene knows that his whole life is shown to his brain by a computer program. He mentions that the beef he is eating doesn't exist in reality but he still enjoys the taste of it.