Fuel is the stuff that provides the energy to move forward (both literally and figuratively).
Literal fuel - like vitamins and gasoline and protein and coal and water - enters the system of the living organism or machine and triggers a train reaction of events that supplies the needed energy for performance.
Figurative fuel is the stuff of consciousness and motivation, the things that push us toward our goals. Figurative fuel doesn't apply to machines. Yet, for living organisms it is just as important as the literal fuel. Figurative fuel looks/feels like purpose and hope and love and loyalty and ambition and meaning.
With both kinds of fuel, quality matters. Our cars won't run well by putting crappy fuel in the gas tank. By the same token, our bodies cannot perform optimally by loading them up with junk fuel. Similarly, if the things of the heart and spirit that motivate us are low quality or absent, we lack the needed fuel for commitment and performance.
The same goes for organizations (whether they be families, churches, schools, businesses, or nations).
Quality fuel and regular refueling is the stuff of high performance.