The reasoning here is a bit like this: If your phone is a knockoff, you don’t really have an iPhone. So if you can’t know that your phone isn’t a knockoff, you can’t know that you have an iPhone. In this case, we start from the plausible claim: If you’re in a simulation, there’s no spoon in front of you. By the same sort of reasoning as in the iPhone case, we get to: If you can’t know you’re not in a simulation, you can’t know there’s a spoon in front of you. The same applies to everything in the external world.
