nvestment Principle (Ia.6) The tendency of any well-developed skill to retard the growth of similar skills because the latter work less well in their early forms-and hence are used so infrequently that they never reach maturity. Because of this, we tend to invest most of our time and effort on elab- orating a comparatively few techniques, rather than on accumulating many different ones. This can lead, at the same time, both to the formation of a coherent and effective personal style and to a decline in flexibility that mav be wrongly attributed to aging