It is like a blind person thinking, what am I so blind about? Unless he can see, he will never understand what being not blind is.

In the same way those who are in ignorance can never know what they are ignorant about unless they become not-ignorant.

But nevertheless, they can make a guess like the blind man, "I bang into objects all the time." Others don't so there is something that is wrong with me. Likewise, those of us who are ignorant can make a guess. These are called philosophers.

Try checking out Immanuel Kant's Critique of Pure Reason. There he discusses the limitations and defects of human reason. How it is impossible for a man to see the reality behind objects.

Schopenhauer then completes the task left behind Kant by saying that it is possible to see the reality only if we ultimately succeed in the denial of the great will or the thing-in-itself. One can slowly weaken the individual will and can put an end to the phenomenal existence. Then the noumenal world alone remains.