At each moment of our life, we are not only living the fruits of our past actions, but also creating those for tomorrow. Similarly, at each moment we are preparing ourselves for the lives yet to come. Prarabdha or destiny is caused by the actions done in the past.
Thus, if our prarabdha is a sorrowful one now, let us perform such acts today that can determine a happier life for us in the future. The law of destiny does not explain to us how, even while we live the preordained and prarabdha-controlled pattern of circumstances, we can have in the immediate moments a freedom to create afresh (purushartha or free will). This positive approach is an essential part of the law of Karma.
A happier tomorrow is built only when we assert our will to live a divine life today. By living rightly today the divine values of love, kindness, tolerance and mercy, you will ensure a more noble pattern for your future. By honest introspection, you can detect your wrong tendencies and eliminate them through constant, deliberate effort.
We must start and constantly keep on the right path to reach the goal of supreme good. Thus, the law of Karma when understood correctly, is the greatest force of vitality in Vedantic philosophy. It makes us architects of our own future.