The presence of delusions is one of the findings that characterizes psychotic disorders and severe depression. However, delusions may also be found in people without severe mental illness.
A delusion requires both of the following:
(1) the person has a strong belief
(2) the belief continues to be held despite incontrovertible evidence that it is false
The level of attachment to the belief can vary, as well as the level of certainty.
The level of evidence against the belief can also vary.
In some ways most religions can be viewed as shared delusions.
Whether or not the delusional thinking contributes to bad decision making depends on:
(1) how attached the person is to the belief
(2) why the person continues to hold the belief despite evidence against it
(3) the level of insights that the person has
(4) if the belief leads to the person to behave in a way that harms the self or others
(5) if the person has other biases linked to the delusion such as jumping to conclusions (a tendency to make decisions with certainty based on insufficient information)
Some beliefs are held by people with issues such as stress, anxiety, anger and depression. The belief may be an attempt to cope with the problem.
