There are many things that we simply don’t perceive at all, even in our immediate environment. We can’t see behind ourselves or around walls or over distances; we can’t see outside the visible spectrum; we can’t hear outside a narrow range of sound; we can’t smell a fraction of the things our dogs can.
In addition, we sometimes perceive things inaccurately -- this happens whenever we misinterpret what our senses detect. This covers a wide range of things, from feeling pain in phantom limbs to being upset when we mishear a comment from someone else.
False memories of things we may have originally perceived correctly degrade our understanding even further.
Finally, using sound logic based on false assumptions can lead us to drift even further from reality, e.g., believing that the world is flat.