I agree that karma exists and I believe that if a person commits a sin, he will definitely get the result of it in some form or the other in this birth. But it is not always the case that we have to go through the mistakes of our ancestors. Yes, it is possible that some aspects of our life may change due to their decisions, but this much is certain that if we have done good and worked hard, we will definitely get the result, even if it takes some time, but nothing wrong will happen to us if we have not done bad to anyone.