Well, yeah, that's kind of the problem. If you're the kind of person who can FIRE, you're not the kind of person who'll be happy on permanent vacation at the age of 40. It's nice to have that option, but many people who get into FIRE commit themselves to a lifetime of slight misery instead of learning to be okay with living life when they can. I had these struggles too - I cut corners I didn't need to, and it took me a long time to internalize that I'd rather enjoy my life in my 20s than save money to do nothing in my 40s.
E: I'm editing to say this because like four different people have issued variations of the same response: the alternative to FIRE is *not* not saving! It's saving for your future while not aiming to retire early. Set a good target savings rate that will help you comfortably retire in your 60s, and spend the rest on things you care about. Let go of the mindset that any spending is taking years off your retirement.