Inattentional blindness is a psychological phenomenon where individuals fail to notice an unexpected stimulus in their visual field when they are focused on a different task. This occurs because the brain has limited processing capacity, leading to the omission of information that is not deemed relevant to the current focus. A famous example of inattentional blindness is the Invisible Gorilla experiment, where participants watching a video of people passing a basketball often fail to see a person in a gorilla suit walking through the scene. This illustrates how attention can blind us to obvious details when we are concentrating on something else.