What the law of karma teaches us is an absolute equality. You get payback what you had given at the certain actions in a forgotten time with unknown beginning. There is only a time difference between the receiver and the past giver as present receiver in terms of continuity of the soul. However the continuous soul should be regarded as not a fixed entity but a continuity of consciousness that activates and regenerates a pile of forgotten informations in prior lifes. That is why, when difficulties come, rather than feel pains and be discouraged by them, we must admit that forgotten information from the past has only been revealed by different appearance. Rather, you should be relieved and rejoice because you have paid off your debt.
If you understand that both the luck and the misfortune that have come to you are just paybacks for your actions in the past, you will not be able to exercise feedback of giving back to others out of hatred or pride like negative feelings.
Likewise, equality is not to share exactly same but to give a same attitude toward good and evil. There is no cosmic preference here. God turns the wheel of karma such way. Taoism says,
Tao of Heaven has no taste and no intimacy.
天道無味無親