"What is the use of having brains in our profession? I know well that I have it in me to make my name famous. No man lives or ever lived who has brought the same amount of study and natural talent to the detection of crime which I have done. And what is the result? There is no crime to detect, or, at most, some bungling villany with a motive so transparent that even a Scotland Yard official can see through it."
That is Sherlock Holmes in 1881. At the very beginning.
He hasn't gotten the merest whiff of Moriarty yet, and he's complaining about how boring the detective business is, practically on day one. He's plainly had enough experience with the real world of London crime and Scotland Yard at this point to make at least some generalization about the matters, but, still, this is Sherlock Holmes AT THE BEGINNING.
And when, ten years later, he just goes "Heck with detection, I'm going mountain climbing. Maybe there's an abominable snowman up there. I wonder what's up with Tibetan Buddhism?" Was he really just taking a three year vacation? Or was Sherlock Holmes, like a certain author, actually just done with it and moving on?
Like any other human being, we'd like to define Sherlock Holmes as a constant. We're lazy that way. We resist letting the children in our lives stop being children in our heads, even when they're thirty-five. Keeping track of the personal evolution of everyone we know is more than a brain can handle. And a guy like Sherlock Holmes, with an active, seeking mind who says things like "I abhor the dull routine of existence. I crave for mental exaltation?" That guy is gonna go through some changes.
It's funny how fanfic often portrays Watson, the damaged vet, as the sexual one when we have this guy center stage. Sherlock Holmes may have said "I should never marry myself" -- which is actually just acknowledging that a long-term committed relationship wasn't going to work for him -- but the mysteriousness that he ascribes to women in "The Second Stain" would actually attract him like a moth to a flame. And remember that "flame-like" woman he actually takes on as an accomplice for "Illustrious Client?" I am definitely not trying to say Sherlock Holmes restrained himself to the hetero-normative by any means. Quite the opposite. This guy was horny for life in all its pathways.
Sherlock Holmes, as much as he proclaimed a focus on detection, really wanted to know everything about everything. He retrained himself, the brain-attic metaphor, etc., because he knew that omniscience was practically impossible to attain, but think about his profession for a minute. It wasn't really about crime at all, which was why he took non-criminal cases. He just wanted to find things out, to dig into some previously unknown alley of human experience with each new client. No wonder he was chasing monkey-men and pseudo-vampires by the end of his career.
Sherlock Holmes did not need Joe Chill to shoot his parents in an alley to become a detective. He didn't need his father murdering his mother over a dalliance with a math tutor. And he certainly didn't need some boarding school mystery with a cult that shot hallucinogenic darts to become who he was.
Sherlock Holmes just had to be really, really, irritatingly bored. Detective, explorer, undercover government agent . . . musician, chemist, martial artist . . . all of the other paths weren't stars in the distance he followed, but roads he was goaded upon by the pricking of the boredom stick. Had he lived in 2021and started life with video games and dozens of streaming on-demand channels, maybe Sherlock wouldn't have been nearly so interesting when all was said and done.
But in 1881, things could get pretty dull. Motivatingly so.