For the purpose of putting an end to stress, all that needs to be known is how to create skillful kamma and then, once that skill is mastered, how to create the kamma that puts an end to kamma.

"The workings of kamma are complex — more complex, in fact, than is indicated in [MN 136]. Their complexities would have posed a challenge for the Buddha if he had wanted to construct an explanation of stress and its end based on first principles, for a theory of kamma would have been a logical place to start. Thus he would have been required to give a full explanation of how and why kamma is complex.

But because his teaching was teleological, aimed at actually putting an end to stress, he needed to explain only what was necessary toward that end: the ways in which past and present kamma shape experience. Although past kamma can influence the conditions on one’s sensory experience, the actual stress or lack of stress experienced by the mind is the direct result of present kamma — the act of following or abandoning clinging and craving. For the purpose of putting an end to stress, all that needs to be known is how to create skillful kamma and then — once that skill is mastered — how to create the kamma that puts an end to kamma [AN4:237]. Thus there is no need to account for all the complex interactions of kammic results. A knowledge of general principles is enough."

~ Thanissaro Bhikkhu "Skill in Questions: How the Buddha Taught"