To give a diagnosis means that the psychologist is identifying the condition that a patient has. While a diagnosis may, over time, come to be seen as incorrect or incomplete, there is no "right or wrong answer" given in response to the diagnosis itself.
If the psychologist is unable to obtain a complete and accurate assessment of the patient's condition, the diagnosis may not represent an accurate evaluation of the situation. A patient may not cooperate with the evaluation process "either out of embarrassment or through denial that symptoms of a mental problem even exist." If a patient intentionally withholds information or provides incomplete or untrue answers to questions during the assessment procedures, the evidence collected may lead to an inaccurate diagnosis. Such answers might be considered "wrong", but they would be given before the diagnosis of condition was determined.