Many people can drive a cab, including many who are unemployed, but not so many can get permission to do so in many major cities in Europe and the US. Imagine much of the economy organized like the taxi industry.
以出租车执照为例。许多人都能驾驶出租车，包括许多失业者，但没有多少人能被获准在许多欧美主要城市中从事这一营生。试想大部分经济都采用出租车业类似的组织形式。因此大部分形式的经济刺激政策都不可能催生更多的出租车，除非行业准入限制被放宽。