But more importantly many people thing that the way to become rich enough to retire early is to penny-pinch as much as possible, but that makes you quite miserly and you won't be able to enjoy anything.
You don't have to penny pinch, but you do have to spend less than you earn so that any excess income would go into savings, and sure one of the ways to get there faster is to put more money into your investment/savings/retirement plan faster, so you can accomplish by spending less and/or earning more. It does not mean that you have to suffer, but sure, suffering could be a way to reach that FIRE status earlier.
From my point of view, it seems a bit presumptive to imagine that suffering has to happen in order to reach FIRE status early, even if suffering would likely expedite such process of getting to FIRE faster.

I like this part of your statement, because some people who have extra funds to save for their future by investing it, don't do that but rather they spend the extra cash on their wants believing that tomorrow will be better than today without them having to invest for a better tomorrow. How is that possible. I have always told me friends that I will prefer to limit my flashy lifestyle and invest those extra cash on bitcoin to grow my portfolio for F.I.R.E.
Since I am in my youthful age and still have the strength and very agile, I will keeping on working to generate more funds and cut down my expenses so that I can invest more in bitcoin for my old age, because I am able to work and earn good income, why will I be spending without planning for the future when I wouldn't have this strength and flexibility to work the way I am working now. If I don't save and invest for F.I.R.E, I will might end up in a poor state by that time.
If only a lot of people can look at it this way, when we were teens, we went to school to graduate in other to get a better life, or we learn a skill so that it can take care of us when we are on our own. If you don't take your studies serious or your skill, you wouldn't be a professional in it and wouldn't be able to earn good pay to take of your and family because the kind of job you will be doing will be a low paid job. Same applies when you have started working and earning. Since you have discretionary income, if you did not plan for it and invest...at old age, you will have nothing on you and living poor will only be your option.
I learned this from my Uncle, he had a good job in the sea port and was rich but he didn't invest a dime, because he didn't plan for F.I.R.E and was enjoying himself to the fullest, when he retired, he got broke within 5 years and now he is a poor man. It's what you have today that you will use to plan for tomorrow.