Brain Filter

Your brain ignores a lot of sensory inputs. We blank out while driving but still reach our destinations with no incidents, we tune out smells pretty quickly (no matter how bad), we tune out physical sensations (you ignore how your tongue is resting in your mouth, you ignore it but you always see your nose), we ignore the the second ‘the’, we hit autopilot at work, etc.

It's probably an evolutionary trait that evolved from a need to be vigilant against unique sensory input, like sudden movements and noticing things that aren't supposed to be there. We’re good at recognizing patterns, and tune things out to reduce overall taxation from sensory inputs so we can instead focus on novel inputs.