The only thing that can ever really be shared is love. You are only ever attacking yourself. And you do not really have any ability to effect another person. They are incapable of being attacked by you unless they first attack themselves and then put the effects of the attack onto themselves using their own mind.
Nobody has ever really attacked anyone because it's impossible. There are no real victims.
So this idea that you actually "do something" to someone, and have to then "pay for it" with some kind of revenge-balancing system, is bogus.
The only way it might operate is that if you believe that you are attacking someone else, but are actually attacking yourself, IF you don't learn that you are attacking yourself and undo YOUR OWN self attack, then you might need "lessons" that show up externally in order for you to learn to love yourself. But it can't be happening as some kind of attempt to "balance" a debt or to ATONE for some sin that you really committed. The only purpose can be the UNDOING of the belief in sinfulness.
Karma is a belief that sin is real. Sin is not real.
The only "karma" you need be concerned with is what you are doing TO YOURSELF.