“Every day we learn something new and absorb additional information and knowledge.
But it is not as simple as adding something to a storehouse.
It is a complex process of integration.
Knowledge influences the knower.
The knower changes with what he learns.
One may also forget what was known, but the impression made by the knowledge cannot be effaced.
One can forget everything that one has learned, but one cannot wipe out the effect it had on the personality.
Which, incidentally, explains why it is forbidden to put to shame a scholar who has lost his ability to remember.
It is assumed that what he once knew remains as a subtle, ineradicable influence.”
From Pebbles of Wisdom from Rabbi Adin Steinsaltz