God is never so turned away from man, and never so much sendeth him new paths, as when he maketh ascent to divine speculations or works in a confused or disordered manner, and as it adds, with unhallowed lips, or unwashed feet. For of those who are thus negligent, the progress is imperfect, the impulses are vain, and the paths are dark.
Zoroaster, quoted at The Herb Dangerous, Part II: The Psychology of Hashish by Oliver Haddo (Aleister Crowley)
If you held the belief, child, that I knew everything that hid under every stone and leaf, I must disappoint you. I may have my own understanding of how the art works, sharpened by long years of memory, but I do not know how it will work for you. There is a reason I call magic an art, rather than a science. I might guess, but in guessing too hastily I might influence, or even diminish, your talents—taint you with my predictions.
J Kelley Anderson, Casting Shadows [Amazon]