"The foolishness of God is wiser than the wisdom of men."
~1 Corinthian 1:25
"The fool doth think he is wise, but the wise man knows himself to be a fool." ~Shakespeare (As You Like It)
The greatest good you could do for another person is to free them from their own thoughts. Not replacing their thought with another thought, but giving them a taste of infinity, a savor of the nectar of pure consciousness, liberated from the bondage of any thought at all.
"Guru" means "the light that removes darkness." A real Guru is the reverse of conventional Western notions about teaching. The myth of our tradition begins with the darkness of the unknown. Then an authoritative teacher imparts the "right" concepts to believe in, leading us to the light of knowledge.
But spiritual truth is just the opposite. The darkness is the known. A Guru plays the role of trickster and fool, startling us out of the shadowed labyrinth of our mind, into the light of the Unknown.