Humans have five senses, and they are used to pick up impressions of their surroundings. There are individual differences. These can be caused by the sensory organs themselves, for example because of red-green blindness or high-frequency hearing loss. But they arise mainly during information processing in the brain, because several areas of the brain work together in a complex way to produce the sensory impression. The current emotional state, previous perceptions, what one is currently paying attention to and much more have an influence.

Two identical cameras with wide-angle lenses would, within their physical capabilities, produce a very similar photograph of a moment in time. However, two people often have very different perceptions of the same situation even with similar sensory impressions: for example, one person would perceive that a blackbird is chirping loudly while another has the starting engine of a car in focus. This often leads to misunderstandings in communication, because both have experienced the same physical situation and yet report differently about it. We even disregard the role of memory and not even talk about any assigned meaning. Both bring even more variation to the game.