Reaction is an animal tendency that we inherited through our phylogenetic evolution from animals. It’s purpose is survival. This happens at sub-conscious level, with knowledge of the past memories. Action proactively is a human character. This happens at the level of intellect or higher. Wise people act and the unwise react. In reaction past baggage of memories play a big part.
In action Atmic reflection plays a significant role, through mind (buddhi). Here are two example for us in Bhagavatam, Kamsa and Parikshit. Both are destined to die. Kamsa is destined to die in 10 years (through the 8th pregnancy of Devaki) and Parikshit in 7 days by snake bite. Kamsa reacted, lived in fear, killed several innocent children in the process and ultimately could not escape the destiny and died in fear.
On the other hand, King Parikshit, who was cursed to die in 7 days, acted calmly, did not curse the curser in retaliation (though he had the capacity to curse), made no excuses, apologized for his error in judgment, intensely looked for productive way to spend those 7 days. He was grateful for the advance warning, listened to Bhagavata for 7 days narrated by sage Suka, and attained Moksha.
In one of the Yaksha prasnas, Dharmaja was asked is, “What is the most amazing thing in the world?”. Dharmaja said that while death is always following every human from birth, most humans act as if they are going to live forever. Death is a shadow of life. This awareness of the presence of this shadow, puts our priorities of life in order. Thus we have a choice to be the Kamsa or the Parikshit. A choice to be reactive or proactive, to be in fear reactively or be at peace like King Parikshit and be proactive..
Parikshit welcomed the inevitable and made sure he spent every minute of his remaining days in search of realization and attained Moksha. This is a lesson for most of us, who have forgotten the impermanence of the body and permanence of the soul. We spend and waste time in external worldly pursuits that enhances our inadequacies and fears. Instead we should understand the impermanence of this body and feel the urgency to make the most out of this life and do activity (sadhana) to make us realize our true nature and reach the destination called Moksha, like King Parikshit.