In our innumerable past lives, had we ever committed this type of immutable karma? The answer is yes. Therefore, we can be as virtuous as we like in this life, but retribution may still await us if we cannot purify all our negative karma from the past. Once this type of karma matures, there is no escape from bearing its effect, albeit temporarily. Does this mean that virtuous karma we have accumulated in this lifetime will go to waste? Certainly not. It will also bear its own fruit. However, if virtuous karma is not powerful enough and ripens slowly, it is possible that we may have to suffer first before enjoying any reward.
[Excerpt from Luminous Wisdom Book Series ~ The Right View : On Cause and Effect]