I just retired 2 months ago. I had 3 triggers, each one wasn't sufficient by itself. They were:
1) A couple of close friends who were younger than me died suddenly. The one that really hit home was a co-worker who was the office jock. They found melanoma inside his nose & he was gone 12 months later.
2) The job went to S**t. I'd always enjoyed what I was doing but got stuck in a position where I had to work 12 hours a day and try to persuade people I had no line authority over to do things I thought was stupid. When I wasn't doing this, I was putting together layoff lists and trying to figure out how to explain to my management that 10 people couldn't do 20 persons work.
3) Because of 1 & 2, I started researching this and other boards and found out that financial independence had snuck up on me. I had been planning to hold on until my pension maxed out but I found out I didn't need to.
So far, its been the best decision I've made in a long time. My first 2 grandchildren were born the first 2 months after retirement. Their parents don't live close to my house so its been a lot of fun being there for their first two weeks and helping around the house. If I'd still been working, my DW would have been doing this while I was stuck at the office.