I think FU Money is an attitude that can be had without the funds to back it up if you believe in your own skills/potential. My example:
In the summer of 2007, I ran a one-week summer soccer camp for high school kids in my area at my school. I had to set up a separate business entity to do it right, but all my proceeds went to benefit the team I coached at that school because there were no funds for the athletic program. I did this same thing the year before and everything went just fine. This year, however, they wanted me to "rent" the field from the school even though they knew all my proceeds went back to the school's soccer program. They told me it was to cover the cost of mowing the field for the week where they would've just let it keep growing until school started again. I thought this was fairly reasonable, but not the brightest move by any means. (Let it be known that the principal was an absolute tool. She had no clue what she was doing, and this was one more piece of evidence.) Anyway, I arrive on Monday for my soccer camp, and the fields have not been mowed. My first day with the kids is in knee-high grass and weeds. Needless to say, I was pissed, especially if that's what I was paying rent for. I stormed into the office to give her a piece of my mind and left to mow half the field that night myself with my push mower so I wouldn't look like such an idiot the next day. The rest of the week went okay; a parent came and mowed the rest of the field for free. The principal came to collect the rent money from me late in the week; I had a bag of coins for her to count out if she cared.
I realize that's a lot of lead-in if you've read this far, but my tale is about one-third in. After the weekend, I get notified on Monday that the school board would like to talk to me about my behavior and interaction with our principal during that week of soccer camp. Apparently, my reaction to the indignity of the fields not being mowed was a sign of insubordination to them. (This is weird because I was a separate entity that was renting the field from the school as instructed. The fact that I happened to be employed there should not have been a factor.) They set up a meeting where I had an opportunity to apologize and come to terms with being the bad guy in this situation. In this special hearing, I stood firm to my beliefs as a soccer coach, a teacher, and a human being that I was in the right. I gave them a list of reasons why it would be foolish to terminate my contract for the upcoming school year and the difficulty they would face in doing so. It felt really good to let them know what a terrible decision they were about to make. After a brief deliberation, I was welcomed back into the room to hear my fate of termination. Here's the best part, and they didn't know this was coming. My wife also worked there as a teacher and resigned immediately. We were young, had recently bought a house, and had no secure income outside of our teaching gigs. Their only response were mouths agape. The principal had the gall to speak, and in her stupidity uttered towards my wife, "Can I get that in writing?" The middle of July is not an ideal time to find replacements for the English and Math Department Chairs as well as new soccer coaches.
The following year was what we call our "lean" year. Mustachian principles had to be used to survive, not thrive with a large savings rate. I began selling some of my video games, old CD's, and books online as a side gig. I did construction work for my brother. I did some substitute teaching (pretty rough sometimes because I took any and all gigs available). In my new temporary job--as in-school suspension room monitor--I was allowed access to the internet all day, every day in what amounted as my search for a new full-time job. I got hooked up with a teacher head-hunting firm and they found a great opportunity for me in the private sector making twice what I made at my other school. The best part was that my wife got hired on at that new school, too. We doubled our income, moved out of wintery Michigan for Florida, and live biking/walking distance from our employment. As for our bumbling principal, she was demoted back to being a fifth-grade teacher the year we moved and is no longer with the school (I'm not sure why).
Having an FU attitude allowed us to pursue even better opportunities elsewhere. I can tell you that school was so conservative, they never thought anyone would be so "reckless" about their future, and that made all the difference. Now, we're just about 9 years from FI and an option to RE which I will likely take. My wife may continue to teach; she finds it fulfilling.