The Tzimtzum (Divine Withdrawal) does not work in only one direction.
The world is not an illusion, a "maya" or hallucinatory dream.
It does have a real existence, but as a Divine shield, God as Elohim.
The concealment manifests itself in the form of a reality, a reality that hides the Divine Light.
To give another inadequate illustration:
I can hide or disguise myself in a number of ways: by wearing different garments, by putting my hands in front of my face, by covering my eyes.
Whether I conceal myself from myself or from others, I remain the same one.
Thus YHVH Elohim is one, the sun and shield, the two names of Divinity.
The aspect may be of one who gives forth light or of one who is in darkness, but the manifest one and the hidden one are the same one.
Because the hiddenness is indeed real, creatures may feel separate and enjoy the freedom to determine their own essence and to do some things on their own.
It is like learning to play the piano.
Both hands have to be taught, each one to play independently of the other.
At the same time, they have to play in harmony, in absolute coordination.
For one hand to play its own music would be disharmony, wrongness.
In other words, the freedom allowed to man to determine his own essence is like the independence accorded to the hand to play its own music, even though without coordination there is no harmony, no rightness of execution.
Our freedom to do as we choose is also the freedom to err, to get out of rhythm and to do the wrong thing.
–Rabbi Adin Steinsaltz
–From In the Beginning by Rabbi Adin Steinsaltz