Clearly a counterproductive multiplication of books:
Hearing these things, despite the true knowledge which Nólemë had and spread abroad, there were many who hearkened with half their hearts to Melko, and restlessness grew amongst them, and Melko poured oil on their smouldering desires. From him they learnt many things it were not good for any but the great Valar to know, for being half-comprehended such deep and hidden things slay happiness; and besides many of the sayings of Melko were cunning lies or were but partly true, and the Noldoli ceased to sing, and their viols fell silent upon the hill of Kôr, for their hearts grew somewhat older as their lore grew deeper and their desires more swollen, and the books of their wisdom were multiplied as the leaves of the forest.
J.R.R. Tolkien (The Book of Lost Tales, Part One: Part One)