Beliefs, ideas, images, and verbal descriptions that we consciously or unconsciously form from our experiences and which (when formed) guide our thoughts and actions within narrow channels. These representations of perceived reality explain cause and effect to us, and lead us to expect certain results, give meaning to events, and predispose us to behave in certain ways. Although mental models provide internal stability in a world of continuous change, they also blind us to facts and ideas that challenge or defy our deeply held beliefs. They are, by their very nature, fuzzy and incomplete. And everyone has different models (that differ in detail from everyone else's) of the same concept or subject, no matter how common or simple.