Puranas are case histories of Vedas. Puranas bring the esoteric statements of Vedas that can only be understood by learned few, to the level of common man in the form of easily understandable stories. These case histories clarify the values of Vedas. Here is one such case history of acting vs. reacting.
Life presents with two kinds of events. Things that can be changed and things that can not be changed. With the things one can change, one should put 110% effort and gracefully accept the results (nishkama karma). With the things inevitable like the aging, death and the like, we should learn to gracefully accept it and make the best use of our remaining abilities to do as much good to the society as possible, find salvation and peace at the end. Here are two examples . One who mis-managed and the one who properly dealt with.
Both Kamsa and Parikshit were cursed to death. One after more than 9 years (through child from 8th pregnancy of Devaki) and the other one in 7 days. With impending death Kamsa reacted with emotion of fear and Parikshit acted through discrimination of intellect and acceptance of ultimate reality.
Kamsa tried to avoid the inevitable by developing hatred and killing all the new born children. Inspire of this he ultimately faced with death and died in fear. On the other hand Parikshit after being cursed, fearlessly did introspection, accepted the reality of death and made best use of the left over time. He approached sage Suka, listened to Bhagavata and attained Moksha.
Life presents these choices to us frequently. These two examples in Bhagavata are examples on right and wrong way, acting and reacting. Let us act rather than react.