That is the infallibility of fate. If you defy it, weren't you always meant to defy it? Do you not see rahbu, here in your midst?
Thakr, Source:MLP, Chapter 45

Rahbu is the Saddle Arabian concept of fate. Their society practically worships fate as a deity-like entity, and believed that the chosen of fate, the Acanthi, were able to shape the future. Through this "divining" capability ancient Acanthi predicted Equestria would destroy the world and bring about eternal winter. That prediction led to war.

This turned out to be a self-fulfilling prophecy, as the war became a major contributor to the series of events precipitating the apocalypse.