I don’t have an answer, but I do have a couple thoughts that may constrain the possibilities. First is that causation, in my mind, is not like dominoes. Rather, as I understand what the Buddha taught, cause and effect are like two sheaves holding each other up. So kamma and vipaka arise together. I think of it like a system, where the cause feeds the result, and the result feeds back into the cause (i.e., vipaka further feeds volitional action).
Second, in reviewing the suttas regarding causation, there’s discussion of consciousness and nama-rupa. Each feeds (and causes) the other. As I read it, the outflow of consciousness is “designation-contact” and develops new kamma. This outflow of consciousness feeds into nama-rupa, which then has an outflow of “impingement-contact”, or a kamma inflow back into consciousness. This cycle itself is not grounded in a more basic substance or medium, but is self-creating and self-sustaining, fed by kamma.
I hope that this is consistent with a wonderful discussion of the “hidden vortex” found in Ñāȵananda’s The Magic of the Mind, and I would also look at Bikkhu Bodhi’s The Great Discourse on Causation.
there is no mistery. Kamma operates because there is a -self.
- Attachment to -self = more new kamma
- Dettachment from -self = no more new kamma
- End of arising of -self = end of kamma
this is the way
I think it’s important to keep kamma and dependent origination separate. The latter was the Buddha’s description of how suffering arises. About kamma he said (as has been mentioned in this thread already by others) that it’s one of the imponderable subjects. He definitely did not say that kamma works along the same lines as dependent origination. He encouraged understanding of dependent origination but said we should let go of the question of how kamma works.
If I take a lighter (A), flick the flint to spark a flame (B), and then take the lighter to a candle (C), touching the flame on the wick (D) then the candle wick alights (E).
There is a chair.
When I take two legs of the chair away (A),
Balance ceases (B).
When one stops clinging (A), to an unhelpful view (B), then the release of stress becomes apparent (C).
It is by this mechanism and medium that kamma operates.
AN3.77 has
“So, Ānanda, deeds are the field, consciousness is the seed, and craving is the moisture.
So in this example, you have the intentions(deeds) but not the craving. Thus the seed doesn’t grow.
When you have craving in the future, the seed will start to grow again.
If this is true, and a Buddha is without craving, his kamma seeds also cannot grow and ripen. This means that his pains, wounds, sickness etc can also not be explained as kamma vipaka like i have seen happening.
As I said earlier, I think it’s better to focus on something verifiable here and now.
But in any case I believe kamma seeds starts ripening when a person is born. His birth specifies that he has this genetic disorder/illness and the country he is born, etc. Thus Buddha ‘suffered’ from wounds,sickness because karma started ripening before enlightenment.
Sentient beings are the owners of their deeds and heir to their deeds. Deeds are their womb, their relative, and their refuge. They shall be the heir of whatever deeds they do, whether good or bad.
Do you believe kamma is related to suffering? If it is, then which process describes that relationship? Why isn’t it dependent origination?
AN3.76
How is bhava defined?
“If, Ānanda, there were no deeds to result in the sensual realm, would bhava in the sensual realm still come about?”
“No, sir.”
“So, Ānanda, kamma is the field, viññāṇa is the seed, and taṇhā is the moisture.
The viññāṇa of sentient beings—shrouded by avijjā and fettered by taṇhā—is established in a lower realm. That’s how there is rebirth into a new state of existence in the future.
(Iterates for every realm)
That’s how bhava is defined.
kamma, leading to continued existence and rebirth, is separate from dependent origination?
This is from Ajahn Brahm’s book, Dependent Origination.
⟹ : is a sufficient condition (is always a cause) for
⟸ : is a necessary condition (at least this is needed, something else may do the rest) for
avijjā ⟹ saṅkhāra
saṅkhāra ⟸ viññāṇa
viññāṇa ⟹ nāmarūpa
nāmarūpa ⟹ saḷāyatana
saḷāyatana ⟹ phassa
phassa ⟹ vedanā
vedanā ⟸ taṇhā
taṇhā ⟹ upādāna
upādāna ⟸ bhava
bhava ⟹ jāti
The bolded lines / necessary conditions are related to the behavior of kamma.
It means “if there are saṅkhāra/choices, viññāṇa may arise, but not necessarily.” This is the setting of the field, and the planting of seeds depends on the field.
But those seeds are yet to grow without their moisture, taṇhā.
Clinging is a necessary condition for continued existence, but this won’t happen without the other conditions: the field, seed, moisture, which are all three sufficient together, conditioning continued existence. With ignorance being behind all of this.
Then, there is birth, aging, death, and suffering.
So we should let go of how suffering works? The Buddha was referring to irrelevant parts of kamma, it’s extremely important otherwise, because how could you describe an ethical system or a practice without it. Just because we don’t know the literal scientific processes behind it doesn’t mean it’s not related to your life, desire, birth, death, and suffering. The same can be said about the process behind entering a new body, we may not know exactly how, and it may be a waste to figure it out, but we can see it does and see its connection to suffering.
No, we should let go of how kamma works (which is the OP’s question)
“There are these four inconceivables that are not to be conjectured about, that would bring madness & vexation to anyone who conjectured about them. Which four?
…
“The [precise working out of the] results of kamma.…"
AN 4:77 Acintita Sutta | Inconceivable
and we should definitely try to understand how suffering arises through the process of dependent origination.
I’m just advising to keep these two concepts separate, because that’s what the Buddha did.
according the sources, the imponderable about kamma is knowing its origins and results. It has nothing to do with its relation with the -self.
The Buddha taught about how kamma works, its manifestation and the relation with the -self.
Kamma operates while there is an acquisition of a -self. This is a truth of the Dhamma.
I have pondered successfully without being an arhant. Anyone can do it.
Dependent Origination only can be completely understood by arhants. While there is any trace of attachment the DO cannot be understood in all the extent. One should know this when he is investigating the DO because these limits are implicit in ourselves.
There is no necessity to be engaged in D.O. for whatever thing despite it offers a whole frame to understand the Reality. Because we cannot in real terms, only in an intellectual way, and this is always is a failed machine.
The root of karma lies in emotions.
Say you hurt someone in a past life. A thousand lifetimes later they are reborn as a dog, and you a human. You can try to make Peace with the dog, but if you don’t, the dog may bite you. Such is the ripening of karma due to consciousness carried over many lifetimes.
The reason why a human birth is considered so rare is because there is a level of purification before one can get reborn as a human.
But don’t think all harm or evil comes from karma. There was once a Master named Jesus Christ who had no karma, some believed He was a Buddha, and he said “they hated me for no reason.”
The same thing happened to Siddhartha, when he had difficulties in his life, it was not due to his own karma, but his decision to help others. Sometimes with righteousness comes persecution. Such isn’t always the result of one’s own karma. The intention of the miscreant is there, however, and it lies in their own emotional ignorance, as they create evil karma for themselves. So let’s be good.
the root of kamma is the ignorance of delusion of -self. And the kernel for kamma is the will, volition.
Even a fly has a kamma. Emotions are part of kamma but no the roots of kamma.
That makes a lot of sense.
I’m thinking, though, if emotions are the root of being, if all beings have emotions, from bacteria to Solar Stars, then karma would too overwhelm by emotional impact. Someone who knows there is no Self to grasp onto could still cause good karma based on their emotions of happiness, or negative, by anger. Except my statement is quite broad, but I find it possible that all beings do have emotions of some sort, that’s what makes them alive, as phenomena, and capable of Enlightenment.
From Cetanasutta
Mendicants, what you intend or plan(i.e thinks about), and what you have underlying tendencies for become a support for the continuation of consciousness. When this support exists, consciousness becomes established. When consciousness is established and grows, there is rebirth into a new state of existence in the future. When there is rebirth into a new state of existence in the future, future rebirth, old age, and death come to be, as do sorrow, lamentation, pain, sadness, and distress. That is how this entire mass of suffering originates.
Let’s see if the following example works:
“I want to eat ice cream” ← Intention
Support for consciousness (Consciousness seed)
“I like Vanilla taste” ← Desire
“I see advertisement about Ice Cream” ← Desire
…
…
“I have enough money to buy ice cream” ← Other conditions
Tasting Ice Cream ← Result/Vipaka ( New existence) - New consciousness experience
If there is no supporting conditions(enough money, ice cream available at the shop etc), the result would not come. But that doesn’t mean it went away. Consciousness keep growing and growing with new nutrients(desire). The result may not be the taste of ice cream either.
Naturally, I don’t have an answer for it 
The analysis of kamma is usually done in terms of psychological events in the mind but it seems to me it goes beyond it. I am puzzled by the fact that effects of kamma can also be external events that life throws at us, perhaps even in future rebirths. That makes us part of an unfathomed cosmic process .