People, people. This is not how karma works. What goes around does not in fact come around, and it is by no means a bitch. Karma is not a retributive force: it does not have a personality, and it cannot be summarized with the “what goes around comes around” statement that everyone likes to apply to it.
Generally put, you accrue Karma. Your actions cause karma to collect around you, or to dissipate away from you: the more negative actions you take, the more karma you accrue, and the heavier your metaphysical mass. Eventually, you become so metaphysically heavy that you sink down in the cycle of rebirth, and end up returning to earth as a rock or a cat or something of that nature.
You may only decrease your mass through successive rebirths and actions that are good: these cause your metaphysical mass to decrease by releasing your karma into the wheel of samsara. The better the life you live, the less your karmic debt (that karma carried to the next rebirth) and the closer you get to nirvana.
That’s another thing, nirvana is the extinguishing of everything: your karma, your mental perturbations, the very thing called your provisional self. Think of it as a uptopian state of non-suffering. Nirvana extinguishes everything in a single blissful release, but the kicker is that you are nothing after that. Nirvana isn’t heaven, it’s nothingness.
Anyway, stop perpetuating this nonsense of Karma as retributive or whatever. Karma isn’t causal, you are causal. Your karma simply determines the situation into which you are born.