Our life, human life is 100% precisely governed by inscrutable laws of karma. As we sow so shall we reap, nothing less or more says law of karma!
Whenever positive residual balance of karma from previous manifestations suddenly fructified in present life, one became lucky. One could even win a big lottery.
Winning the lottery did not result from karma indulged in present life, yet we reaped fruits of karma performed in earlier manifestations. How lucky?
From the above analogy it is clear that human beings must all the time indulge in positive karma, good karma to not only improve our present but also future.
We cannot modify karma but we can definitely nullify a negative residual balance of karma from previous manifestations by indulgence in good karma, positive karma all the time. This way we can reduce our anticipated, predestined sufferings.
Luck always results from a positive residual balance of karma in our kitty from previous manifestations undertaken by our soul atman, the spirit existing in heart.
The law of karma and the related doctrine of luck become clear only when we indulged in spirituality detailed in Bhagavad Gita or Upanishads (independent spiritual treatises).