Indefinite knowledge or incorrect interpretation can result from defective sensation. The defect may lie in the senses themselves, as a physiological fault in perception, or in the indefiniteness or blurring or contradiction in the sense stimuli, as found, for example, in optical illusions. The synthetic ability of the mind to piece together, or form a whole, from incomplete data often leads it to make errors. The mind sees what it is accustomed to seeing. Such errors in interpretation or imprecise knowledge may lead to incorrect judgements and as a result, to accidents. Unfortunately, when the habit of seeing what is desired to be seen instead of what is actually there is brought to bear on developmental and social issues, illusions may be maintained in official reports, particularly those showing satisfaction and giving positive evaluations for what is being done to address world problems.
An example in navigation is confused hearing of foghorns near high shores where echoes are thrown back, or in visual radar-control of fast-moving, apparently collision-bound aircraft, where rational after-images of blips can occur to the controllers.