I think people can be intimidated at learning new skills for what appears to be a relatively complex system. Whether it be a computer, a vehicle, cooking, or house maintenance, all those are complex on the whole. But, when you break these things down to individual components they're not really too complex.
I learned how to build computers at a young age because video games were a hobby at the time. My parents didn't care to upgrade the computer, so I would Frankenstein used parts I could scavenge cheaply in order to make games run. I still recall a time when I had our dinky old computer so overclocked I had to leave the side panels off with a giant floor fan running across the system just so it wouldn't overheat and melt itself.
This was at the cusp of the internet when access to information wasn't readily available, and with only one computer once our system was down I had no way to research what I was doing wrong. I can still feel the dread in the pit of my stomach when I changed out a part or configuration, hit the power button, and nothing happened. I would scramble to somehow fix the machine before my parents chewed me out for "messing it up again." To them, this tinkering was pointless and potentially damaging. In hindsight, it set me up for a life of useful skills. Now a days, I can fix any problem with computers that arise with ease. It was stressful in the early years, but every roadblock was a learning opportunity.
I take that life lesson with everything now. I'm not a great mechanic, but when something breaks I sit down and slowly figure out how to fix it. With information so abundant now, fixing the car is not a matter of if, but when.
It's the same as why we learn a variety of skills in school that many will not even touch again. Math, science, history, biology, etc. Our brain starts to build connections from previous lessons learned. Lessons I've learned with computers helped me understand car systems. Learning car systems have helped me learn home maintenance systems. Chemistry has helped me to be a better cook. Biology helped me understand how to best cook a specific cut of meat. Both helped me understand why diet fads are a joke, and what I actually should eat to be healthy.
Everything ends up being interconnected at some point due to the laws of physics. I truly believe we do ourselves a disservice when we fear making a mistake because a task is too daunting. One poster above mentioned, why would I not pay to change my car oil if I am FI? Simply put, that skill might relate to an unexpected and unrelated task down the road. Plus, it will give you confidence in situations that would leave many others giving up and asking for help. "Yeah, I can do this. Hand me that wrench." I can't wait to have more time in FIRE to develop these skills even further.
In short, this is the badassity part of MMM. By making yourself self sufficient, you empower yourself to accomplish more than you ever thought possible. Our current economic system encourages specializing to keep the economy churning along much more efficiently. Saving a lot of money in an index fund is only one aspect of breaking that mold and taking advantage of everyone else's close mindedness.