The results in current life is Prarabdha, the actions lead to Agama

Indeed complicated are the behaviours and manifestations of Karma. We are taught that the current birth is the result of that past Karma. We are exhausting our current (Prarabdha) Karma. Even Jivanmuktas who stop accumulating Karma, have to live on until their Prarabdha Karma gets exhausted.
Sanchita Karma on the other hand is Karma from the past that has expired.
And Agama Karma is what most of us humans are accumulating, which will show results in future birth.
But there is also the apparently direct experience that when I sow the seeds, the crops grow. If I do not, they won't. If I study hard, then I'll get good marks, else I won't.
It really does seem so, but is it truly so? If it was indeed as simple as that, why does direct experience also report results to the contrary. We all have seen that we prepare hard at times, and yet the result is not in our favour. You slip when running the race, or your train is delayed to the exam location. Or you make that silly mistake in the exam or project.
Why do you think one of Krishna's best advices was to not get anxious about the result. That you don't have any control or even the right to it. That indeed the best approach is to surrender all efforts to God. This we because of two reasons:
- The purpose of life is to get moksha and stop the constant accumulation of Karma. Surrendering effort as service to God stops any expectation of results, and helps stop the accumulation of Karmic results that have to bear fruit later.
- The mechanics of the working of Karma: It's hard to believe but based on the experience of our ancestors who developed the theory of Karma, all the results that you get today were actually earned by efforts in the previous birth. There is also an exception to the rule that if the effort was intense, it shows result early i.e. in the current birth itself. This is difficult to explain and has a level of subjectivity. It is also difficult to prove from the standpoint of direct experience.
But also understand this is why Life does not look fair which all of us experience. People seem to get results despite not having earned them.
First lesson is to accept that they have earned it indeed, even if in the past life. And that for their wrongdoing now, they will get the resultant punishment, if not now then in the next Life.
Life and Karma are really most fair!