People with cotard disorder (the belief that one is dead) or mirror agnosia (the belief that it is not one’s own reflection in the mirror) are not persuaded by what most of us would consider sound reason. If someone with cotard disorder is challenged with the fact their bladder feels full to contest the delusional belief, they respond with a verbal defense such as “that just proves dead people’s bladders get full”. People affected by such things as cotard disorder and mirror agnosia are not lying. In fact, they are quite sincere in their denial of reality based facts. We all know people that weave their perceptions into words that are not necessarily connected to reality, what we may not be aware of is just how common this practice is.
In order to get a better look at ourselves we need to make sure we don’t confuse sincerity with accuracy. Although we tend to believe what our senses are capable of projecting, perception can be distorted by any number of factors from biological to ideological, so sincerity is no guarantee of accuracy. If we see through a distorted or broken lens, that view appears real to us even if it doesn’t agree with reality. We might try to prop up the confidence we have in an accurate bead on reality by thinking that physical damage or chemical imbalances in the brains of these “other” people are the cause of all delusional thinking, but evidence suggests the contrary. What we would call “normal” people with undamaged physiologies hold beliefs that not only test the bounds, but outright contradict reality.
Many things beyond mere physical damage can shape what we are tuned to see. Our perception is powerfully influenced by local environmental factors such as our genetics, epigenetics, family, relational circumstances that happen at critical periods in our lives, local climate and so on. In addition, our senses are limited by nature. Our visual senses are not equipped to process the full spectrum of light into an image. Beyond visible light there is radio, microwave, infrared, ultraviolet, X-rays and gamma rays. The point is that the portion of reality we see is small by comparison to the whole spectrum in many ways. Another example is the information pipeline we receive from our social environment is often a convoluted mess communicated with imprecise words. The fact that our senses have a limited capacity to translate the whole picture coupled with the fact that we share those distortions with each other makes it difficult to sort fact from crap.
In his book “The Folly of Fools: The Logic of Deceit and Self-Deception in Human Life” by Robert Trivers, outlines the fact that prosecutors confronted with DNA evidence based on current science still believe the people they convicted before these methods were available are still guilty. Once established, we tend to defend our beliefs by discounting conflicting evidence and overweighting confirming evidence. This tendency is no different than the person with cotard disorder stating that dead people’s bladders get full. It is also why the mindsets and relationship dynamics that are prevail during our childhood so powerfully affect most our world view and experience throughout life.
With all of this in view it seems the most certain thing we can rest on is an element of uncertainty.
 Cotard disorder is a delusion where the individual negates themselves in some biological way. This may involve the belief that they are dead, or that they’ve lost their internal organs or they are immortal. Some with Cotard’s syndrome have the notion that they are possessed or that other people’s identities are false. It is named after neurologist, Jules Cotard who described it as the “délire des négations”.
 This tendency to hold beliefs by discounting some evidence while inflating other evidence is sometimes called confirmation bias.