Every simulation is indistinguishable from reality within the context of that simulation. Without an external POV - the simulation cannot be experienced as anything other than real.
Anything that is indistinguishable from reality is essentially reality. If it walks like a duck, quacks like a duck, and you don’t have any way to access any data that says it isn’t a duck - then it’s a duck.
When you read a book, you begin a simulation. You construct a world and characters and use the book as a guide for the rules of that world.
You are the Matrix.