It's a story/analogy written by Christine Miserandino from But you Don't Look Sick.com that helps healthy people to understand what living with a chronic illness is like. It's the best analogy I've read and it's where the term 'spoonie' comes from.
Spoonies are people that suffer from fatigue for whatever reason.

Created and read by Christine

I've tried to find an audio version with no success, there are plenty of YouTube versions but not everyone has unlimited broadband so...here's a audio file of me reading the story.