I am not FIRE but I wanted to offer some insight.
I have been, 2 times in my life, able to stop working for an extended period of time. These were temporary situations.
Both times, I went in to big depression.
The problem I found, was that I had nothing to do. And, when I tried to do more with other people, I ran in to roadblocks because they were still on regular monday-friday 40plus hour work schedules. So, I was limited to seeing them on the weekend (if they were free) and so, a majority of my time was with nothing to do. Sure, I could have joined a club or something but I didn't.
In my mind, and this may go against the grain here, I never want to retire. I always want to work at least part time until I die. I never want to work full time for life mind you. But I never want to be completely without a job to go to. I find it keeps me grounded in real world life. When you have no anchor to the normal heart-beat of the rest of the world, it seems I was lost and alone. Maybe cause I am single as well.
I wish there was a method for FIRE that included working your whole life. I'd rather not FIRE and instead, do a half FIRE. Instead of building u a huge nest - egg that FIRES me (trading huge amounts of labor to get there), I'd rather start working part time now and do so for life.