The harm of not relying on the teacher
It is inevitable for one to fall into hell endlessly for slandering, and abandoning the teacher.
It is stated in The Essence of Nectar - Stages of the Path of Englightenment that, one will drift in miserable realms endlessly.
After we have established a dharma connection with our teacher, where the teacher-student relationship is founded on just a mantra with few words that was taught verbally, or with only one verse of the teachings given, it is without a doubt that abandoning or slandering the teacher is of the weightiest nonvirtuous karma.
Translated from the excerpt from The Heart of the Path