First of all, not all Kamma has to ripen as a matter of necessity. Although it has the tendency to ripen, it does not ripen inevitably. Kamma is like a seed. Seeds ripen only if they meet the right conditions. But if they do not meet the right conditions they remain as seeds; if they are destroyed they can never ripen at all. Similarly, it can be said of kamma that kamma pushes for an opportunity to mature. It has a tendency to mature. If kamma finds the opportunity then it will bring its results. If it does not meet the right conditions it won't ripen. One kamma can even be destroyed by another kamma. So it is important to understand that our present way of life, our attitudes and conduct, can influence the way our past kammas mature. Some past kammas are so powerful that they have to come to fruition. We cannot escape them no matter what we do. But the greatest number of our past kammas are conditioned by the way we live now. If we live heedlessly, unwisely, we will give our past bad kammas the opportunity to ripen and this will either hinder the good kammas from producing their effects or else cancel out their good effects. On the other hand, if we live wisely now, we will give our good kammas the opportunity to mature and bar out our bad kammas or weaken them, destroy them or prevent them from coming to fruition.