Cairns made in the economic cycle, in order to increase employment and expand demand, or even a group of people employed trench, and then another group of people employed to fill ditch.

• 凯恩斯提出在经济萧条周期，政府为了增加就业，扩大需求，甚至可以雇一批人挖沟，再雇另一批人填沟。