Herbert Spencer

People … become so preoccupied with the means by which an end is achieved, as eventually to mistake it for the end. Just as money, which is a means of satisfying wants, comes to be regarded by a miser as the sole thing to be worked for, leaving the wants unsatisfied; so the conduct men have found preferable because most conducive to happiness, has come to be thought of as intrinsically preferable: not only to be made a proximate end (which it should be), but to be made an ultimate end, to the exclusion of the true ultimate end.