User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-6951062-20130321230637/@comment-3146930-20130321231025

The Fates are able to see things as they can be and how they must be. Sort of like how prophecies are vague and have the possibility for multiple meanings, so to does a person's future. Percy saw one possible future his life could take, but not the definitive future his life would take. If it was, then the concept of choice would just be an illusion.