User blog comment:SayuriDarling/The Mark of Athena Official Discussion/@comment-88.253.70.13-20121010205444/@comment-3146930-20121014142202

The Fates see possible futures, as the future is always changing. Think about it like this, the first Great Prophecy talked about a choice Percy would make about trusting Luke or trying to stab Luke himself. The Fates knew all the possible events leading up to that point and they knew Luke would die one way or the other (either kill himself or Kronos would destroy his body), so they cut his string. However, depending on Percy's choice, the future would change. When Percy saw them, he saw a possible route his life could take, but not the only route.