In reality this confidence is entirely unfounded.  A threefold difficulty exists.  In the first place, young people know very little about themselves and their abilities.  When the day comes on which they discover their real strong points and their weaknesses, it is often too late.  They have usually been drawn into the current of a particular vocation, and have given too much energy to the preparation for a specific achievement to change the whole life-plan once more.  The entire scheme of education gives to the individual little chance to find himself.  A mere interest for one or another subject in school is influenced by many accidental circumstances, by the personality of the teacher or the methods of instruction, by suggestions of the surroundings and by home traditions, and accordingly even such a preference gives rather a slight final indication of the individual mental qualities.  Moreover, such mere inclinations and interests cannot determine the true psychological fitness for a vocation.  To choose a crude illustration, a boy may think with passion of the vocation of a sailor, and yet may be entirely unfit for it, because his mind lacks the ability to discriminate red and green.  He himself may never have discovered that he is color-blind, but when he is ready to turn to the sailor’s calling, the examination of his color-sensitiveness which is demanded may have shown the disturbing mental deficiency.  Similar defects may exist in a boy’s attention or memory, judgment or feeling, thought or imagination, suggestibility or emotion, and they may remain just as undiscovered as the defect of color-blindness, which is characteristic of four per cent of the male population.  All such deficiencies may be dangerous in particular callings.  But while the vocation of the ship officer is fortunately protected nowadays by such a special psychological examination, most other vocations are unguarded against the entrance of the mentally unfit individuals.

As the boys and girls grow up without recognizing their psychical weaknesses, the exceptional strength of one or another mental function too often remains unnoticed by them as well.  They may find out when they are favored with a special talent for art or music or scholarship, but they hardly ever know that their attention, or their memory, or their will, or their intellectual apprehension, or their sensory perceptions, are unusually developed in a particular direction; yet such an exceptional mental disposition might be the cause of special success in certain vocations.  But we may abstract from the extremes of abnormal deficiency and abnormal overdevelopment in particular functions.  Between them we find the broad region of the average minds with their numberless variations, and these variations are usually quite unknown to their possessors.  It is often surprising to see how the most manifest differences of psychical organization remain unnoticed by the individuals themselves.  Men with a pronounced visual type of memory and men