During Sherlock's darkest days after the tragedy at the aquarium and John's fury at him, Sherlock realizes that he wants out. He's lost half the people he loves in a span of just a few minutes, and it's burnt him out completely. So, he writes John a note. A letter explaining everything. A letter telling John that it's the end of the legendary Sherlock Holmes. (My entry for the fanfic Friday From the Heart contest)