Here is the more important point about Karma. It does not pick winners or losers. Rather, it seeks fairness and justice.
In order to keep Karma from shifting from your good/positive to your bad/negative, you must make sure that you never let pay-back or personal retribution for past grievances control your actions or cross your lips. Karma is all-knowing and can shift like the winds that blow from a completely new and different direction. Give it up to God and pray for the right and correct thing to happen and for justice to prevail. All simple stuff if you can do it.