In his Iḥyā ʿulūm al-dīn, Imam al-Ghazālī (rahimahu Llah) also said:

The aspirant requires a shaykh and teacher to emulate and to guide him to the balanced way. The way (sabīl) of religion is obscure (ghāmiḍ), and the ways of Satan are numerous and apparent. Who does not have a shaykh to guide him, Satan leads him to his paths. So who seeks the plain way of destruction with no sentinel, let him ponder alone and destroy himself. The independent one (mustaqil) alone is like a tree that sprouts by itself, because it agitates the neighbors. Even if it remains long enough to grow leaves, it does not bear fruit. The aspirant must cling to his shaykh and hold tightly to him.