"Three wishes I have granted you. My service is complete."
"Wait! It's not a wish, it's a question. When I wished for you to heal my shoulder five years ago, did you know that I would be shot again by the same type of bullet?" (1)
"Yes."
"Was I shot again because of my wish?"
The djinn smiled. "No. The Maker has His patterns which I cannot alter. Are you displeased with your last wish now, having had only five years without pain?"
Watson considered. "No, it was enough."
"You are a strange mortal," the perplexed djinn declared, but with respect.
(1) Baring-Gould hypothesizes that Watson was hit by a jezail while helping Holmes on a case not long before the events of SIGN. I'm inclined to agree, since Watson says he had had a bullet pass through his leg "recently" and at least seven years had lapsed between Maiwand and SIGN – hardly recent. Also, although we get some specific details about his shoulder in STUDY, there is no mention of a leg wound. Why would he bother to mention one but not the other?