नादत्ते कश्यचित् पापं न चैव सूकृतं विमुः-- God never rewards the virtuous nor punishes the wicked. -- Bhagavad Gita, Ch. 5, 15.
The law of causation, or law of Karma includes the law that the like produces the like, or that every action must be followed by a reaction of similar nature. If I strike a blow on the table, the table will react upon me with similar force. If I strike harder, I shall receive harder blow in return.
In the chain of cause and effect, it can be shown that each effect is latent in the cause and each cause is latent in the effect.
We do not have to blame our parents for our misery and sufferings. It is our own Karma that produces its results in the form of joy or sorrow, pleasure or pain, happiness or unhappiness. It is compensation.
Everything that we possess in this life is the effect of our previous Karma or action, both mental and physical. Our present character is the resultant of our past and our future will be determined by our present acts. Neither God nor Satan is responsible for our pleasure and pain, happiness and misery. Thus, all the inequalities and diversities of characters can be scientifically explained by this law of Karma. In the face of this universal law of Karma, there is no room for the hypothesis of predestination and grace which is accepted by the majority of orthodox Christians. The hypothesis of predestination and grace teaches that God, the Creator of all, settles the destiny of man before his birth. He preordains before the birth of each man and woman what he or she will be in future. The whim of the Creator makes one sinful or virtuous, before the time of one's birth. But this hypothesis destroys our moral responsibility and personal freedom.
He who obeys the law of Karma is more moral and more virtuous than one who blindly obeys the Ten Commandments. He stands on a more rational ground than one who fears the punishment of God. He shrinks from doing anything wrong, not because it is written in a book or scripture, but because he knows that every wrong action will sooner or later react upon himself and will make him unhappy and miserable. He performs good deeds for the reason that they will bring good reaction in the form of happiness, peace, tranquillity and higher enlightenment.
(..To be continued, 2nd of a seven part series).

Very few understands the hidden meaning of Karma.If one understand the meaning properly there is no reason to complain against anybody.
Aksharma, Jun 13 2016 on k.ekvastra.in