What is the magic ingredient that makes us 'shift'?

Butty what a wise response. There isn't a magic bullet and it is all those things you mention. I remember when my mother was dying and my sister was looking after her, and she had been in a miserable marriage for a long time, she phoned me and said "I'm leaving him". I said "why now?" And she said "I can't do both". And that was it, she chose looking after my mum over coping with her marriage.

My son, who has given us the hardest time over the past 18 months, it is suddenly as if the mists have cleared and he has stepped out into the sunshine. In his case, I think it is the 'love of a good woman' for which I am grateful beyond words.

I honestly don't think this can be categorized. There are as many reasons for shifts occurring as there are people with difficulties; from a long, slow road to recognition and change to a moment's chance meeting with someone, and everything in between.
I think it also depends upon the individual's back-story. This has as strong an impact upon how one deals with 'flights into health' as anything else.