This is a question I have thought about a lot. I really think it depends on who you are. True confession time below:
I had what I like to call a "brush with FI" in my late 20's, early 30's.
My father died when I was 20, and left me a decent sized inheritance. The money definitely demotivated me to some extent, but I did manage to graduate college with good grades in a hard science, but a lot of my drive was gone. I made some facepunch worthy purchases ( new car, a few vacations) but I did invest a large amount of it in the tech boom years, and did very well. I will say that I was not any happier with the money. In fact, I was a lot LESS happy in my 20's because I felt like I was just killing time at work. I felt like I had no purpose really and was just waiting out the years until I had kids. I desperately wanted out of that job and I didn't really think much about what life would be like when I didn't go to work.
When I was in my mid 20's, my investments were doing well, and my husband and I wanted to have children, and we realized the money allowed me to stay home with them with no issues. So I gave my resignation, and after working part time during my pregnancy, I was unemployed for the first time since age 14. It was a wonderful feeling at first, and the first few years of having small babies consumed all my time and kept me busy, and things were going pretty well.
I had planned to stay home for 2-3 years, 5 at the most, but I ended up staying home for 8 years total. In those years, the tech bubble burst, we switched financial advisors to one who was dishonest, and I frittered away a lot of money on stupid kid related stuff to kill time as the kids got older. So between that, and the fact that I was home a lot more time then planned meant that most of that money was gone by the time I went back to work 3.5 years ago.
I learned a lot about myself on those years, but mostly what I learned is that I need to keep busy when not working, and structure my life so that I don't expose myself to temptations. I am not FI yet, but I am what I call "financially secure" in that we could live several years without one of us working and still be fine. My ideal life structure in FI probably includes part time work. I just do better with some sort of structure.
I have a much better idea of what FI will look like for me, which I plan on hitting by age 55 or so. I'd like to drop to part time by age 50, join a choral group, run, volunteer more in the community, and in general keep myself busy. I have a much better concrete idea of what FI will look like in my head than I did at age 25. It is not all sunshines and rainbows, and stress and life will still happen, whether you are working a 9-5 or not.