They taught us that in the military (yes, i went to the military for a few months because it's compulsory in my country):

When you come home from a field trip, all your equipment is gonna be really dirty. So you gotta clean your equipment first, only then yourself.

The lesson i took from it is that we are the tools to clean stuff. And we must be cleaned as well, but only after we've cleaned other stuff, otherwise it would be pointless.

You clean yourself with the shower. You clean the shower with a rag. Now you enter a terminal state of cleaning:

• You clean the rag with a washing machine
• You clean the washing machine with the rag
• You clean the rag with a washing machine
• You clean the washing machine with the rag
• You clean the rag with a washing machine
• You clean the washing machine with the rag
• ...

The fact that there are cleaning item cleaning items implies the existence of cleaning item cleaning item cleaning items, which in turn implies...