“What the Jewish sages recommend is not only a middle way, it is a rejection of extremes in terms of a clear knowledge of how to keep everything, including the extreme, in its proper place.
Consequently, in general, there are no preconceptions about what is the correct conduct for all situations, since the correctness of a way of being is itself only measurable in terms of a specific set of circumstances that may or may not recur.
There is therefore no possibility of fixing a single standard of behavior.
If anything is clear, it is that a rigid, unchanging way is wrong.
Furthermore, this principle of movement, of constant change, is the principle manifested by the soul itself in its life on earth.
To be sure, a person needs a special teacher or a great deal of guidance in order to be able always to find the right measure; usually choosing the correct way grows out of the soul’s continual oscillation from one extreme to another.
This pendulum swing of experience brings about a certain synthesis somewhere in the middle — although too often it is an artificial middle, merely halfway between good and evil and neither one nor the other.”
–Rabbi Adin Steinsaltz
From The Thirteen Petalled Rose by Rabbi Adin Steinsaltz