What is your WHY?

What is one moment that you can say definitively that you knew your why moment? Was it the significant other, THE job, the house or car? Was it leaving someone behind knowing that sometimes you have to walk away from another person even if you loved them. It doesn't have to be a romantic relationship I am necessarily referring to, but any close personal one. Was it a moment you took control of your life? Was it a moment when you said you had enough of _______? Was it a moment from one in a white coat giving you bad news? Was it a moment when you finally looked into a mirror or stepped from the scale in shock... Was it a moment when you asked yourself "why" were you doing __________ or working 'that' job? Or was it a moment when you took steps to better yourself mentally, physically or educationally? Even IF the people around you thought you were crazy and hitting some sort of midlife crisis? How did you know? What did you do about it? Can you share some advice for other's from the 'other side' of the situation?