When a person passes from one level to another, there is an increased danger of falling.
He is no longer secure in the previous level, and can easily fall before he gains a hold in the next level.
This is true, of course, for every change in condition or of level of existence.
For instance, when entering the water to swim, there is a moment when one has to lose balance, disconnect from the secure contact with the ground and be neither walking nor floating.
Transition thus always involves imbalance and danger; it is in passing that one may collapse and lose all.
Thus, too, if someone who is learning some skill — either manual or intellectual — is put into a situation where there is a real difference of approach to the subject, it seems fairly necessary to advise the person to forget all that he had learned previously, because it would only serve to confuse him.
He cannot progress to a higher level of performance without forgetting, letting go of what he already knows.
So that those people, for example, who are intrinsically unable to forget are also those who find it hard to progress.
The passage from one level to another demands a sort of leap, an abandoning of all that was solid ground.
It is a basic feature of human progress, resting on the principle that the interval between points or fields comprises a mode of nothingness, and one cannot proceed from one point to another without losing one’s previous balance, even if only for the briefest moment.
–Rabbi Adin Steinsaltz
From The Sustaining Utterance, p. 13, by Rabbi Adin Steinsaltz