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.