The Lama is integral and essential with regard to practice

"Different lineages and different Lamas have their own particular approaches, and one cannot proceed without advice as to the path one chooses to follow. The Lama is integral and essential with regard to practice, and so all decisions about what is or is not necessary depend on one's own Lama. It would be inappropriate, therefore, to take advice on this subject from a book -- if that book conflicted with the advice one had received from one's chosen Lama."

p16, Roaring Silence, Ngakpa Chögyam and Khandro Déchen, Shambhala, 2002, 1-57062-944-7