Long ago, before I ever became a Buddhist monk, I used to consider karma to be some kind of mechanical law of the Universe that science hadn't discovered yet, something like a psychic law of conservation of energy, or, "for every action there is an equal and opposite reaction." I had the notion that karma had the effect of some sort of cosmic accounting, with our goodness and badness recorded for future compensation.
But after studying Dharma a little I realized that, according to Buddhist philosophy, karma equals cetanā, with this cetanā being a purely psychological state, nothing outside of us at all. A famous sutta in the Anguttara Nikāya (sometimes known as A.VI.63) has the Buddha declaring cetanāhaṁ bhikkhave kammaṁ vadāmi—"Bhikkhus, it is cetanā that I call karma." And of the five khandhas, or "aggregates," which in relatively non-technical Buddhist philosophy constitute the entirety of a conscious being in this world, the fourth of the five, saṅkhārakkhandha, or the "aggregate of karma formations," is identified in the suttas with cetanā.
The most common rendering of cetanā into the English language is "volition," although this may be somewhat misleading. At the very least it may cause English-speaking students of Dharma to see karma in a very restricted way, which limits their appreciation of the fact that karma is of fundamental importance in conditioning our life in each moment; and an understanding of it is very helpful for gaining an understanding of ourselves.
Cetanā as volition should not be confused with mere decision-making, or identified with just making up our mind and intending to do something. It's not so much the shape of the pipes as what's flowing through the pipes, so to speak. It might be more useful to see it more as urge than as mere intention, something more like Schopenhauer's will—although it is not the ultimate Reality upon which everything is based, as Schopenhauer philosophized it to be. Cetanā, and thus karma, is the momentum of our mental energy, the mind's "habit energy." It is the habitual force of our perceiving mind, derived from the past and reinforced by it, which acts as a kind of automatic pilot for running us when we are not entirely awake…which is pretty much all the time, isn't it.
The more mindful we are, which is to say the more conscious we are, the less we identify with the automatic pilot, and the less it controls us and runs our life for us, based upon the past, which is when it acquired its habits. The more conscious we are, and the more in the present moment, the more possibilities and options we are able to see, and thus we can act accordingly, rather than mechanically following the one option that our habitual reaction has served up. If we eventually manage to wake all the way up, and thus are fully mindful, then the habitual mental energy from the past may still manifest itself, but it no longer has any power to control our lives.
We really have little if any control over what thoughts and feelings arise in us. We can maximize or minimize the chances of some sort of mental state arising, by various means, but we really don't know what is going to turn up until it turns up. It is the momentum of karma, based upon the past, which determines what arises in the mind. Only after it arises we may observe it and, if conscious enough to manage it, see whether or not it is appropriate to follow along with this thought or desire. So we may not be able to control what karma brings up, but at least we are able not to be enslaved to it. We can still be free from its rigid, limiting control. All this is one way of understanding the idea that an enlightened being creates no new karma, and thus has no "volition," thereby not adding to the habit energy/momentum already there from the past.
Moha, often translated into English as "delusion," goes hand in hand with karma. Moha is essentially a state of semiconscious stupor which allows our karmic momentum to control us like puppets. In other words, we're not awake enough to take full responsibility, so the automatic pilot, the "ego," does the best it can. So if one is fully mindful, moha as well as enslavement to karma disappears.
The idea of enlightenment in terms of Waking Up is easy to disregard; we may see it as just a kind of poetic metaphor, and let the significance of it slide off us like water off the proverbial duck's back. Yet if we really are wise and devoid of moha, then we really are in a state that is comparable to the ordinary state the way a person who is wide awake is compared to a sleepwalker, or someone who rolls over or scratches himself without completely waking up. A conscious person is aware of many things the ordinary person is unaware of—how often do we feel the cloth against our skin, or hear the sound of the refrigerator, or feel the breeze on our arm? How often do we blink or swallow with conscious awareness? How many of us can see that a feeling of desire or fear that arises (maybe strongly arises) is just a kind of habit that isn't us, but is just a kind of robotic program designed to get us through life somehow? Full mindfulness and full wisdom really are a matter of being fully awake.
Sometimes if I suddenly notice that I'm being unmindful and start being more aware, there is a subtle yet really obvious feeling of being more expanded and more conscious; it really is very similar to snapping out of a dozy, groggy state. Also there is a feeling of loss of limitations, as though invisible walls are falling away. It is a feeling of spaciousness and freedom, with complete freedom being another synonym for Enlightenment. We tend to be much groggier, more limited, and more enslaved than we realize, controlled by semiconscious habits, lurching around like sophisticated robots.
Theoretically we could just "snap out of it" and Wake Up, just start being really alert and take full responsibility for our every choice and action; there's nothing necessarily stopping us from that; but it tends not to work out that way in "real life." Instead, we practice Dharma, which gradually clarifies what faculties we have, allowing us to make a little more progress (if we are sincere about making progress). Instead of relinquishing the ego once and for all, a Dharma practitioner systematically cleans it up and lightens it by replacing crude karmic habits with finer ones, or at least diluting the cruder ones down. It's difficult to go the whole way when we identify with the autopilot instead of with consciousness itself, though. Spiritual progress is a matter of letting go of what is familiar, of that to which we are "habituated"; it is a matter of becoming free, which is scary—at least the autopilot is scared. Waking Up is like death for the autopilot. So again, we wind up taking hesitant baby steps toward being able to "do" what is ultimately effortless.
Enlightenment ultimately is not a result of "doing," and is not the gain of anything. Rather, it is the dropping away of unnecessary limitations, including semiconscious stupor, karmic momentum, and identification with the ego, with "me."
And all this is setting aside the issues of transcendental knowledge, psychic powers, and the notion that karma creates our reality, with some of the habitual momentum of past karma coming from previous lives. That may be true also, but for the present moment it is practically irrelevant; the "law of Karma" applies anyway.
an example of karma and its fruition
(in this case happening very quickly)