Sure you can alter circumstances to an extent and that's probably the best way to live life. But all the good in the world doesn't stop a freak car crash killing you or being struck by lightning. And while being struck by lightning is used synonymously with an act of god, I don't think it actually means you deserved it. That's the issue with the just-cause fallacy. It takes a huge spoonful of selection bias to only notice the people who did deserve it.

In my opinion the idea of karma is a convenient crowd control mechanism to prevent people from taking action to fix their situation when they have faith that the universe will magically balance itself out.