Human reality is a slippery concept. Anyone who wakes up from a vivid nightmare knows what it's like to feel stuck somewhere between a memory and a dream. Those experiences lend credence to the idea that there are limitations to our senses. Perhaps our eyes, ears and sense of smell don't really tell the whole story about the reality all around us.
Perhaps the things and people in our lives are merely illusions. How do we know that any of these objects and creatures actually exist? Maybe they're constructs of our own internal mechanisms, spawned by our subconscious for unknown purposes. The universe could be a hologram, a "Matrix" style computer creation meant to entrap our minds and enslave us to a nefarious purpose.
Scientists and physicists aren't sure we'll ever understand the nature of reality. The deeper we delve into physics, the stranger the mechanics of our universe become. We keep discovering new particles and fundamental forces, from molecules to atoms, that drive our bodies and our world. It's entirely possible that the universe could be made up of dozens or thousands of dimensions that we'll never experience in any direct way.
It's unlikely that the scientific rabbit hole we've burrowed will ever end. No matter how smart our collective species becomes, reality will always be an abstraction that we can never quite pin down.