The Doorman

1. Why does your coffee stop working after a few weeks?
2. Because caffeine doesn't wake you. It blocks the thing that makes you sleepy.
3. Adenosine builds up all day, like tickets piling at a cinema door. Caffeine sits in the doorman's chair.
4. So your brain builds more doors. Same coffee, more tickets get through.
5. Skip it for a week and the extra doors close.
6. How many cups does it take you now?

02). A cinema lobby at night. Tickets (adenosine) pile up at the door all day; the doorman lets them through and you get sleepy. Caffeine sits in the doorman's chair and the tickets pile up unpunched. So the brain builds more doors: the same cup, more tickets through. Skip a week: the extra doors close.