To explain such subtle teachings in all their fullness to anyone who will not be able to understand them or to feel as interested as the student does, would be foolish. Nevertheless, he is not the proprietor of them so he cannot keep them solely for his own use; nor is he so separate from others that their inner fate is not his concern. If someone comes who asks questions sincerely or needs comfort spiritually or seeks guidance in bewilderment, the student must give what he can. But he must give it prudently, not pouring out one drop more of his knowledge or power than is needed for the particular person at this particular stage in evolution. There is no necessity to keep truth jealously guarded, as in medieval times, nor to rush to the opposite extreme and give everything to everyone.
-- Notebooks Category 1: Overview of the Quest > Chapter 6: Student-Teacher > # 534