According to the cognitive-behavioural treatment approach client's with certain psychological disorders (e.g. depression or personality disorders) tend to have faulty assumptions and misconceptions. They may be caused by past experiences and are not adapted to the actual situation of the person.
Typical examples of cognitive errors (according to Aaron Beck) are:
Dichotomous / Polarized thinking
Taking it very personal and generalize it as a personal trait instead of an individual, single mistake.
To draw a negative conclusion in the absence of supporting information. Focussing only on negative "proofs" of a position, neglecting all kind of alternative positive aspects of a better outcome.
Example "My husband has not spent time with me tonight. So he must have a girlfriend and he will leave me right now."