No sutra, tantra, or shastra speaks of any being ever attaining
perfect Buddhahood without having a spiritual teacher.
We can see for ourselves that nobody has ever developed all the accomplishments of the stages and paths by relying on their own efforts and abilities alone.
All beings, ourselves included, are very inventive in taking
wrong directions. But when it comes to following the path of
liberation and omniscience, we are as confused as a blind person
wandering alone in the middle of a deserted plain.
No-one can bring back jewels from a treasure island without relying
on an experienced navigator. Likewise, a spiritual friend is our true
guide to liberation and omniscience, and we must follow him with
This is accomplished in three phases: firstly, by examining
the teacher, then by following him and finally by emulating his
realization and his actions.
"The Words of My Perfect Teacher"