It was two events, within a couple of months of each other.
I'd been struggling with dysphoria since age 5 but didn't know what it was until I was 19. I looked into the options then but they were absolutely awful if you're going from F to M, so I didn't think I'd ever be able to do anything about it. Instead, I stuffed myself back in the closet, got married, had a couple of kids, and tried my best to figure out how to live as a woman. (27 years later I still don't have a clue how to do that).
My marriage had been in trouble for a while and I was generally dissatisfied with my life. Then to add insult to injury, as my 40th birthday approached one of my daughters grinned in my face and said "You'll be a little old lady soon!"... and I really pictured what that would be like. I saw myself as a 70-odd-year-old woman in a retirement home, sitting in one of those high-backed chairs they have, wearing a chintzy dress, stockings and comfortable shoes, whilst some young nurse smiles at me and tells me that we'll do some knitting later. I found myself overwhelmed with a sense of despair and regret at having wasted my whole life living as the wrong gender, and now I was too old to do anything about it so I'd just have to slide into my grave wearing a (pick your own expletive here) dress. That thought horrified me; I couldn't bear the thought of wasting my life like that.
And then a couple of months later, completely out of the blue, a news site posted a time-lapse video of a teenage trans guy showing how miserable he was before transitioning, going through all the awkward intermediate stages, before finally looking thrilled with the outcome once he'd successfully transitioned. I saw in his face the same pain I'd been experiencing all my life... followed by the euphoria of putting right what went wrong & finally being able to live his own life.
It was like opening the floodgates.
I felt a sense of regret at all those wasted years during which I could've been in his shoes. I realised that a large proportion of what was wrong with my life was due to me trying to live in a way that is completely unnatural with me. I was 40 years old & I'm not getting any younger, so I felt a sense of urgency to get started with my transition if I'm ever going to avoid being that despairing little old lady. I wanted to fix this whilst I'm young enough & healthy enough to do so. I didn't want to remain married to my husband but if I got out of this relationship I couldn't bear for my next squeeze to be yet another straight man who would view me as a woman & who would focus on all the body parts I've hated all my life. I knew the only way I could fix the vast majority of what was wrong with my life was to transition. I hated the thought because I'm very private and transitioning would mean I'd have to tell lots of people about something very private I'd been battling to hide since the mid-1970s. But it had to be done: I couldn't continue living as I was.
So after a couple of weeks of turmoil I went to the doctor and got a referral to the gender services. A couple of days later I told my husband (he mocked and belittled me, and told me as far as he's concerned our marriage was over). He then pressurised me to tell my kids, and they reacted terribly, calling me a freak who will die alone.
But I don't regret it for a single second. If my family reacted badly, that reflects poorly on them as people. Haters are going to hate, with or without my help.