"John," said Sherlock earnestly, "if I — if I’m not quite —" he stopped and tried again — "John, whatever happens, you will understand, won’t you?"
At the time, John had not realized the full import of those words.
Sherlock did not live to be 100.
But John would be haunted by the memories even when he was 99.
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AU: Where Sherlock and John meet as kids and become the best of friends, and Sherlock does not fake his Reichenbach death but actually sacrifices his life for John’s. Also, in this version, Sherlock’s a year older than John vs. Doyle’s version where John is 2 years older than Sherlock if I remember correctly (And for those of you who couldn’t tell, the quotes are from Winnie-the-Pooh, A. A. Milne’s original book version)