I've been retired for just over a year, thinking about it a lot lately.
The "retire to something" debate - I think it is all about personality. I read so many FIRE stories before I pulled the trigger which made me quite anxious - 'oh no, that person was bored and went back to work after 6 months/1 year'... what if that happens to me?
Well, it turns out, I'm still me. I happen to have endless curiosity about so many things, and I like to read up on many things, play, computer program for fun, etc. I realize now that I should never have worried about my state of mind. I sort of 'talked myself into' an idea that I was going to seek out contract positions for 2-3 months of full-time work here and there. After a couple of months off, that seemed ridiculous and completely unnecessary to me.
And I thought I would worry about money - and in fact it is quite the opposite. After years of scrutinizing every purchase to save everything I could, I find I now have an 'abundance' mindset. Within a few months of quitting I started to realize the 'big picture' money (housing, food, transport) was all well under control and I could really stop worrying about the little things - $100, $200 here and there for fun items/activities wouldn't make any substantial difference, even some thousands for travel (when that's a thing again).
I find MMM was right on with his comments that you begin to make decisions without money being a factor - e.g. 'would I do this contract for free?' - no? then why should I take it? On the other hand, I'm contributing to open source projects, occasionally thinking 'shouldn't I find a way to monetize this?' - no, don't need to, I have enough money; I'll do it just because I enjoy it.
But, to each person according to their personality and their circumstances. Those who are not reasonably 'self-directed' types might find it different. Those on "lean FIRE" might not be so comfortable with the money. But if you regularly find interest in projects, volunteering, travel/activities within your budget, you are likely on a path for a happy successful FIRE.