The memory of our past action evokes a habitual pattern. This is described in the Buddhist scriptures as being like the face we make when someone says “sour” or when we think of sucking on a lime. Since we have already experienced eating a lime and tasting that sourness, when we just think of that experience, our face makes a puckered expression as if we were eating a lime right now. The habit is formed out of memory, from that point of view. The memory of certain things is pleasurable, and certain memories are painful, We often reshape our present situation according to that habit, or ape instinct, as we might call it. It becomes easier to repeat the pattern again and again. Instead of starting fresh with something new, we can go back to what we’ve done in the past. This is what we mean when we say that we are governed by karma.

From The Future Is Open: Good Karma, Bad Karma, and Beyond Karma, page 17.