Still unpacking karma from Each Moment is the Universe: "Human action appears on the surface of life, and the next moment it is gone. Zen teachers sometimes say, 'Just be present, here and now!' so you may think this means when you do something you should just take care of human action that appears on the surface. But that is really a messy way of life. If you pay attention only to what manifests on the surface of life, you don't understand human beings, because there is something else - unmanifested karma.
Unmanifested karma occupies the basis of human existence. Whether you realize it or not, whatever you do, your action leaves behind a kind of smell in the depth of human life. We have to take responsibility for our behavior, whatever it is, good or bad, right or wrong, because even though our actions disappear from the surface of life, the smell of what we have done is still there as unmanifested karma. If you don't understand that there is unmanifested karma, you cannot understand the depth of human life, and you don't realize the importance of your actions.
Everyone carries the unmanifested karma of human action from the beginningless past as a sort of inheritance or property. It's not something like original sin; it's completely nothing. You simply cannot put any label like good or bad, right or wrong on unmanifested karma, because it is completely beyond the moral sense. So I use the term neutral nature. This karma is always present in your life, stored in your body and mind. If it doesn't appear on the surface, no-one knows it's there. You don't know either, so it doesn't bother you. The fact that unmanifested karma doesn't bother you is its neutral nature.
No-one knows how to open the door to that big store-house of karma at the depth of human life, but there is something that can open the door - time and occasion. When time is right and conditions are arranged, something happens. The door suddenly opens, bubbles come up to the surface, and human action appears."