GROWTH
In the phase of life immediately following sexual maturity, human beings form the belief that they are highly capable and physically unassailable. This semi-delusional sense of selfhood is developed through childhood and adolescence, as the human becomes increasingly coordinated and skilled. It is a function of Object Confidence that humans expect to continue to "progress", and the realization that this is not what is to happen, that in fact there is to be a reversal of this process, is the source of a great spring of sadness and anxiety. We grow, in fact, less confident. Our stride and reach grow shorter, we learn the things we cherish can be stolen, scratches heal more slowly. We know that we are ugly.
Worse than this is the realization that there is no concomitant return to innocence. We lose everything: beauty, vigour, arrogance, our parents; and we continue the incontrovertible slide away from childhood, the repository for all our fantasies of goodness.
This is what it is to be a member of a species of animal who's foremost tenant is betterment, progress, always unto goals; but who's fundamental principle of design is entropy.