When the Âtman creates a new human life, the karma for that life is coded into the DNA. Without changing the DNA, it is impossible for the individual to escape the fruits of that karma. This means that the entire life of an individual is predetermined at birth. One has freewill, but it can only be exercised within the confines of the karma generated existence. In some cases, the individual has enough intelligence from the latitude given in the prescription of karma to make the decision to stop living an individual life.
Jyotish is the science for knowing the karma of an individual life. It is given to us to provide some light on the path of our lives - jyotish literally means light. Through the study of a person's jyotish it is possible to predict the future course of events in that life. It would be cruel to provide this insight without some means of averting the danger that is to come. Hence along with jyotish is given the science of yajña. Yajña is the performance of a specific action that has been designed with total knowledge for the specific purpose of averting some karma. It is effective only when performed perfectly as prescribed and only when the particular yajña that is suitable for a particular karma is performed. Furthermore, the yajña must be performed before the karma has begun to arise - before the bullet leaves the gun. Once the karma has begun to sprout, yajña cannot stop it.