"...inner peace of mind occurs on three levels of understanding. Physical quietness seems the easiest to achieve, although there are levels and levels of this too, as attested by the ability of Hindu mystics to live buried alive for many days. Mental quietness, in which one has no wandering thoughts at all, seems more difficult, but can be achieved. But value quietness, in which one has no wandering desires at all but simply performs the acts of his life without desire, that seems the hardest."
-Robert Pirsig Zen and the Art of Motorcycle Maintenance