Common observation, theory, and past research all point to important relationships between cognitive efficiency and the extent of optimal functioning in the personality as a whole. When there is a disturbance in the personality, there may be some general performance decrement in intellectual tasks or there may be selective impairment. Furthermore, because of peculiarities in overall development, intellectual abilities may fall below—either generally or selectively—the individual’s potential. A man may display a knack for concocting novel ideas but lack the orderliness requisite for a high level of rational analysis; he may be adept at logical reasoning and analysis but be unable to think creatively; or he may be skilful in applying logic to numbers but not to people.