Karma, in general, is the belief, that wrong actions created in the here and now, have consequences, not only later in this life, but in our future lives to come, so that, those that believe that they can "get over" on others, find that in the infinite justice and fairness of God, that God cannot be mocked, nor can God ever be fooled, though mankind fools itself and others, seemingly all of the time, but our karma is the great equalizer.
They say that a little bit of knowledge can be a dangerous thing, and indeed it can be, for those that have a general comprehension of karma, can take such, and manipulate it in a way, in which they then believe that those that are suffering now, are suffering solely because that is their place to suffer, for them having done wrong in previous lives, that therefore, there isn't any brotherly duty to help others in their suffering. While, conceivably this could even be true in a particular case, it does not absolve somebody else that in seeing something that is wrong or destructive, and knowing that they could be of assistance, deciding that they will not do a thing to ameliorate or help such, since they wrongly believe that fate tells us all that there is to tell. Further, those that look upon karma in the wrong way, are the very same people that seemingly are unable to get beyond an "eye for an eye" philosophy, of which, this misreads karma completely, for karma is not about making things even, but rather it is about overcoming previous errors, by making different decisions, and thereupon doing right.
The whole point of karma is the understanding that in life, for every action, there is an appropriate reaction, and when those actions as well as reactions are wrong, then the only appropriate way to overcome that negativity, is to respond with positivity along with actions and reactions that are beneficial and constructive, rather than those being selfish and destructive. After all, the only way to test the sincerity and character of any given person, is to actually test that person in real world situations, of which, some of those tests indeed are going to be incredibly challenging, but it is in the overcoming of these tests, that bad karma is discharged, so that, while few may welcome some of those difficult challenges that they must face, it is in the overcoming of such, that real progress is made.
The fact that we are here, incarnated on this planet, bespeaks for virtually everyone that we have vital tasks to attend to, of which, those that listen to that still, small voice, are slow to anger, fair in their treatment of others, and are diligent about doing the right thing, as best and as consistent as they can, are the very people, that are creating good karma, and good so created, is good for everyone. This world and the people in it, good or bad, are a true reflection of the state of mind, of mankind. Those that in the moments of pure clarity see who and what they really are, and thereupon are determined to do and to be better, will have taken the most important step of liberating themselves from the bad karma that entwines them, into being that which they were created to be, but have lost sight of, which is in the knowing that they are truly the rightful heirs of God.