growing rusty, while those which are not brought before our eyes,
and lie as if superfluous, not being required for common use,
collect dirt by the mere lapse of time, so likewise that which our
thoughts frequently turn over and renew never passes from our
memory, which only loses those things to which it seldom directs
its eyes.

III. Besides this, there are other causes which at times erase the
greatest services from our minds. The first and most powerful of
these is that, being always intent upon new objects of desire, we
think, not of what we have, but of what we are striving to obtain.
Those whose mind is fixed entirely upon what they hope to gain,
regard with contempt all that is their own already. It follows that
since men's eagerness for something new makes them undervalue
whatever they have received, they do not esteem those from whom
they have received it. As long as we are satisfied with the
position we have gained, we love our benefactor, we look up to him,
and declare that we owe our position entirely to him; then we begin
to entertain other aspirations, and hurry forward to attain them
after the manner of human beings, who when they have gained much
always covet more; straightway all that we used to regard as
benefits slip from our memory, and we no longer consider the
advantages which we enjoy over others, but only the insolent
prosperity of those who have outstripped us. Now no one can at the
same time be both jealous and grateful, because those who are
jealous are querulous and sad, while the grateful are joyous. In
the next place, since none of us think of any time but the present,
and but few turn back their thoughts to the past, it results that
we forget our teachers, and all the benefits which we have obtained
from them, because we have altogether left our childhood behind us: