The Guest could be trying to offer a rationale for not being able to accept the coffee --- One potential reason could be that by avoiding giving a blunt negative answer to the kind offering, the Guest could be trying to offer to the Host an explanation on why she/he “is forced” to refuse the coffee (not because it is a non valuable offering for the Guest but because it would be detrimental for the correct fulfillment of next day’ abundant tasks that would require of the Guest to get a sound sleep when going to bed this night -unobstructed by the caffeine she/he would be ingesting into her/his system-.

Source author: Eric Suzán Reed esuzan@sre.gob.mx