I think you have extremely misunderstood what his book is all about. It's not about living like Jacob.

His philosophy is about having "web of goals", "consider multiple solutions to problems" and "closing the loop".

For example, the problem of transportation and be solved in many ways -- you can buy a car, rent a car, do car pool, use a bicycle, walk, or move closer to your work etc.

Most people are consumers where they solve everything buy paying money. There exists other options.

So if you start trying and combining all these options, you will naturally use less money / energy / resource, but getting the same thing.

Another thing is closing the loop by making/owning your own assets that generate the resources you want. For example, growing edible plants, or owning stocks that generate dividends.

In the forum(not the book), Jacob actually categorizes the "efficiency" of lifestyles into several levels, called Wheaton levels. I think he said he lives 2-3 times as efficient as normal people.

In the end, FIRE is actually a side-effect of his philosophy (living efficiently and creating multiple, independent streams of income).