The universe is so big and complicated that mere humans can only perceive a small part of it, and understand even less of it. Sure, our relative intelligence and ability to grasp abstract concepts is what separates is from other animals, but that doesn't mean we understand the nature of what we call reality. What if everything we know is just a simulation constructed by someone else? The possibility was once considered ridiculous, but we're at the point now where we can see how it would happen.
Kurzgesagt outlines this paradox by explaining how close we are to creating simulated universes and intelligence ourselves. What could possibly go wrong? I am reminded of that one night we watched a colony of ants and talked about how they were totally unaware of the intelligent beings watching them. So we turned around, looked up in the sky, and waved to the super-intelligent beings watching us. It's a concept that puts us somewhere between Genesis, Oculus Rift, and The Matrix. Vsauce3 looks into the question even further.
The upshot is that our reality is what we perceive, and we don't know how much we don't know. And we never will. -via Laughing Squid