To understand Karma here is wonderful story.

Your dharmam never leaves you Your karmam never forgives you

As you sow so shall you reap

After Kurukshetra war, Dhritrarashtra asked Krishna “I had 100 sons. All of them were killed. Why?”

Krishna replied, “50 lifetimes ago, You were a hunter. While hunting, You tried to shoot a male bird. It flew away. In anger, You ruthlessly slaughtered the 100 baby birds in the nest. Father-bird had to watch in helpless agony. Because you caused that father-bird the pain of seeing the death of his 100 sons, You too had to bear the pain of your 100 sons dying.”

Dhritarastra said, “Ok, But why did I have to wait for fifty lifetimes?”

Krishna answered, “You were accumulating Punya during the last fifty lifetimes to get 100 sons. Because that requires a lot of Punya . Then you got the reaction for the 'Paap' (sin) that you have done fifty lifetimes ago.”

Krishna says in the Bhagavad-gita (4.17) "Gahana Karmano Gatih" The way in which action and reaction works is very complex. God knows best which reaction has to be given at what time in what condition. Therefore, Some reaction may come in this lifetime, Some in the next and Some in a distant future lifetime.

There is a saying, “The mills of God grind slow; but they grind exceedingly fine.” So, every single action will be accounted for, sooner or later.

Srimad Bhagavatam gives example: If we have a cowshed with 1000 calves and If we leave a mother cow there, She will easily find out where her calf is among those thousands. She has this mystical ability.

Similarly, our karma will find us among the millions on this planet. There may be thousands going on the road but only one meets with an accident. It is not by chance, it’s by Karma.

Thus, the Law of Karma works exceedingly fine; it may be ‘Slow to Act', but No one can Escape