Or: A good verb does not hard-code the location where you do it. Or: A good function does not hard-code the location where you do it. Or: A good function does not know where its inputs come from or where they go. - Functions are verbs. - Where they happen is a preposition. - Verbs should not attempt to hard-code the place they will happen. - IO is about where things come from and where they go. - The `I` in `IO` means "where data comes from" - this isn't a normal function input. - The `O` in `IO` means "where data goes to" - this isn't a normal function output. - Try to decouple your functions from assumptions about where data came from. - The verb "to run" does not know where its user intends to run.