My child asked me how jeep drivers, truck drivers and tricycle drivers in Switzerland and Sweden can prevent the fuel tank from "leaking light" regularly. How to answer?

Children ask you, how do jeep drivers, truck drivers and tricycle drivers in Switzerland and Sweden regularly prevent the fuel tank from "leaking light"? This is an easy answer, because these developed countries in western Europe have good social order and high living standards, and there are few problems of car tank oil being stolen, so there is no need to guard against such problems.