Princess Celestia has seen occasional visions of the future in her sleep, but none so vivid as the ones regarding purple spotted dragon egg. She saw the egg hatch, and the dragon within live and grow among ponies. What's more, Celestia saw key events of the future play out in the most favorable ways possible, all because of that one dragon: the discovery of the Bearer of the Element of Magic, the second defeat of Discord, the second and third defeats of Sombra, and the rise of two rulers who would become invaluable allies of Equestria.
Celestia's visions also showed her where to find the egg. . .