Tirukkural 749: The Fortification

A fort is that which derives excellence from the stratagems made (by its inmates) to defeat their enemies in the battlefield.

Image of Satguru Sivaya Subramuniyaswami
A satguru is needed because the mind is so cunning and the ego is a self-perpetuating mechanism. It is he who inspires, assists, guides and impels the shishya toward the Self of himself.