An especially brave idea is set forth to turn a character on his head and change the status quo in a big way... and the fans revolt. The writer then does a retcon which seems openly apologetic. This is the saving throw. It assures the fans that the character either was not in control of his actions, or he was actually a Doombot, or events were not as they seemed.
Later on, in the list of examples of AST, such as Holmes going over the waterfall (no he didn't), is this:
Jesus... From The Bible... Word Of God says he was trying to fix a Character Derailment, but it resulted in just as much backlash as before.
OTOH, once they went through that, The Bible: New Testament built a much bigger fanbase than The Bible: Old Testament ever got. The Saving Throw must have worked.