I'm not anywhere near an expert, but I wanted to point out that there is a difference (I assume substantial) between someone who drinks 10-15 cups of coffee a week for several years and then goes off permanently and someone who drinks the same amount but regularly stops drinking for a few weeks. The situation isn't exactly the same, but it makes me think of a person who's never run a mile before who can't do it any faster than 10 minutes and a person who runs a mile once every couple weeks and says "that's totally not normal; you should totally be able to run a mile in under 7 minutes" (whether you 'should' be able to as a level of physical fitness or not, it's unreasonable to expect of a person on their first attempt).