Aaron Beck's
cognitive therapy is based on the idea that negative
thought patterns are maintained by
logic errors. An example would be telling oneself '
I can't do anything right', which is obviously
incorrect, but can lead to
low self-esteem,
depression, and other
bad things.
Thus, the solution most psychologists employ is to help their clients notice their erroneous thoughts, and how they are leading to whatever problems the clients may be experiencing. For example, in response to the above example, 'I can't do anything right', the psychologist may assign tasks for the client to do, such as painting a fence. The evidence provided by the successful completion of this task will help the client overcome their beliefs that are causing their anxieties.
Many times, however, the client's thoughts may not be incorrect - they might just be accostomed to a 'negative way of thinking'. In this case, the psychologist works to develop a more optimistic personality in the patient.