This essay entails basic forms of Cartesian epistemology, specifically relating to his evil demon hypothesis. Descartes’ evil demon entails that an evil demon is creating an illusion, or simulation, of the world around you, and this is a perfect simulation. How do you defeat that demon and realize that the world around you is a fake construct of that demon? By doubting, for Descartes held doubt to be the true arbiter of knowledge rather than certainty.
By doubting that the very world around you is real, you have defeated Descartes’ Demon, because the evil demon hypothesis implies that the demon is creating a perfect simulation of the world around you, if the evil demon hypothesis is true, there would be no rational basis to conclude that reality is an illusion or simulation, and yet some people do doubt that.
By the mere existence of doubt Descartes’ evil demon has been extinguished, it has been defeated, banished even. However, reality can still be a simulation, but merely an imperfect one. Either way, it can be argued that reality is still real because reality is what you can experience, from our POV reality is all there is, and so even if it is a simulation, it is still real from the perspective of the people inside that simulation.