I think karma exists like superstition exists. Putting information in terms of a good or bad outcome when it has no meaning in good or bad, black cat crosses your path, going under a ladder, etc. In karma, it could be guilt or reward. You feel guilt for doing something bad but not consciously put it as bad until something bad happens to you. That good feeling you get about yourself in doing some good then when you get something good, you feel rewarded by correlating the two.