The root causes of cars' poor fuel economy or high fuel consumptions

When we think of cars' fuel consumptions usually we ought to relate it to the spark plugs, fuel pump, fuel injectors, oxygen sensors, map sensors, maf sensors, catalytic converter, or engine wear and tears. These many different factors have made us forget about what driven the fuel consumptions in most engine and that is including cars, generators, motorbikes, etc and that is the gas pedal and loads in needs to overcome. 

Most of us overlook what actually driven the engine to consume more fuels because the gas pedal is press more frequently especially in city driving. And of course you have to press even more when the load of the car is heavier or weaker in order to move the car at the pace you want.