... a [besieged] castle - those on the outside want to get in, and those on the inside want to get out. [source]
Actually, I got the quote from a friend at our lunch table. The link to the online source is (a) to indicate where the quote comes from [it's a popular Chines exhortation], and (b) to point to the fact that people in social sciences and humanities can put in interesting quotes in their scholarly articles. I can only envy them.