Board Thread:Questions and Answers/@comment-7888499-20151022220452/@comment-27281875-20160407173018

IMO, Attractor Field are certain fixated events on a group of worldlines, which stood next to each other, or in divergence number they are grouped closely. The death of a person which is affected by Attractor Field is fixated and cannot be changed unless they escape the attractor field itself, that's why Beta-Future Okabe aimed for the gap between alpha and beta attractor field, where lies a worldline unknown to other as no one ever observe the future of worldlines in that gap, the worldline aimed is SG worldline.

No such thing as exception ever explained in the story.