http://chuckthisblog.wordpress.com/2014/09/12/these-are-a-few-of-our-favorite-themes-the-intersect-5-of-5/

Six Degrees of Separation. Six times the Intersect, or events directly caused by it, threatened to tear Chuck and Sarah apart. In Marlin the Intersect threatened to separate Chuck, via bunker, from his family and friends and Sarah. In Ring, the removal of the Intersect threatened to separate Chuck and Sarah by sending them back to their respective worlds. In S3, the Intersect threatened to separate Chuck from himself, and therefore, Sarah from the man she loved. In S4, the Intersect threatened to separate Sarah from Chuck, as it had his parents, through a mission to bring down Alexei Volkoff. On the eve of their wedding, the Intersect threatened to separate Chuck and Sarah through death. Finally, the Intersect separates Sarah from herself and shatters Chuck’s world.