There exist mathematical patterns underlaying all aspects of creation.

These patterns provide an infinite set of possibilities which with the use of correct equations can be narrowed down to the most probable ones.

In the first age when many sciences first came into being men were taught by the people who came before them about these patterns.

Originally astrology was used as one of several sources filtered by what can only be called intuitive calculations and other means, the extrapolated result was the most probable outcome ie. the future.

In fact an entire art existed dedicated to husbanding these patterns which you call destiny to provide the most favorable outcomes for individuals, projects and even entire peoples.