it's not stupid. your experience of the universe is dependant on the information and signals your brain and nervous system are capable of processing and relaying to you. right now, you think you are looking at a screen and reading this message, that the screen is "out there", separate from you. it isn't. what you're seeing is a projection inside your own mind that your brain is creating. you are so used to this deception that it's hard to comprehend, even though you know it's true. you will never be free from the confines of your own head.
if you haven't heard of Plato's cave, it's a thought experiment about a man who grows up inside a cave. he never leaves it, he knows nothing of the outside world, he doesn't even know it's a cave. he sees shadows of animals, to him those are the animals' true form, he hears echoes and to him, that's how things truly sound. your brain is the cave you grew up in and you will never experience life outside of it.
the man in the cave could imperically study these shadows, give them names, come up with theories as to where they come from and come up with an understanding functional to him, but divorced from reality. so how do we trust our conclusions about the nature of reality if we can't even be sure we're even seeing it? that's one of the epistemological questions that philosophers try to solve.