When someone says “sour,” it may remind you of biting into something sour like a lime. Since you already have had the experience of eating a lime and tasting how sour it is, just hearing the word sour and thinking about it, your face makes an expression as if you were eating a lime or lemon right now. Habit is formed out of memory, from that point of view. We begin to reshape our present situation according to that habitual memory and ape instinct, as we might call it.
From “The Tibetan Buddhist Path,” a seminar at Naropa University, Summer 1974.