Destiny means the Divine Will guiding the lines of sin and virtue (resulting in suffering and happiness) experienced by the Soul from the beginning of its evolution till its end in Realization.

Fate or Luck or Fortune is the means or process of spending the impressions the Soul gathers while passing through innumerable evolutionary stages, in other words, the Law of Karma; or the automatic forming of Luck or Fate in the next life, according to the sanskaras gathered in this life.

The impressions of every life build the Fate of the life coming after. As a simile, suppose every Soul has to bear a burden of 700 tons (i.e., a certain amount of suffering and happiness which every soul has to pass through) from the beginning of its evolution till the end in Realization. But as the burden of these '700 tons' varies in kind and form, the impressions of the lives vary too, and the Fate of every new life is formed according to the impressions gathered in the last life.

Thus, the experiencing by the Soul of the impressions of the past life means — Fate. Thus the Soul has to pass through a certain number of lives and forms; but as the experiences of every life vary, so do the Fates also vary. Hence, Destiny is One (for every man), but Fate, Luck or Fortune, is different.