The assumption that all the money I'm not currently saving is living expenses and that these expenses will continue growing exponentially really throws this off.
Many of the biggest expenses people have - income tax, mortgage payments, raising children - all decrease in retirement. Also, many FIRE proponents explicitly include plans to reduce these expenses even more, such as by moving to a place with lower cost-of-living.
The assumption that all the money I'm not currently saving is living expenses and that these expenses will continue growing exponentially really throws this off.
Many of the biggest expenses people have - income tax, mortgage payments, raising children - all decrease in retirement. Also, many FIRE proponents explicitly include plans to reduce these expenses even more, such as by moving to a place with lower cost-of-living.