A metaphor is sometimes used by those who philosophise in favour of conservative institutions such as monarchy or English public schools. It is a picture of something like a post standing in the desert, that you encounter when travelling and do not know the purpose of. The argument - false for a number of reasons, including being based on a false analogy - runs that since you do not understand its purpose and it has been there a long time, you should not remove it. "It" being the post and "similarly" the institution.
My question is this: what is the metaphor more exactly? It has a short name that is widely recognised in some circles. If memory serves, it comes from a book written in the 1910s or 1920s, but I do not remember the title or author, or anything more about the metaphor than I have already said.