Books or learning, the common means to human understanding, are not capable of describing the esoteric knowledge of the reality of the Supreme. This knowledge, known as Brahma Jnana, is referred as realisation or enlightenment. Though many have realised Brahman, their attempts to express this experience only reveal the difficulty and impossibility inherent in the endeavour.
Absolutely. The everyday example I always use is sex. You can't really explain to someone what it is like to have sex. You have to have it yourself.