For the longest time, Sherlock thought he was stupid.
But then he met other children.
Then, for a while, he thought he was brilliant. A genius. Intelligence only paralleled by the likes of his stupid big brother and Stephen Hawking
He loved being clever.
It came as a punch to the gut when he realized there were others, just as clever, maybe even more.
Because they didn't always show it. Didn't look it. Hid it. But that didn't mean they were any less clever.
Maybe it meant they were more clever.
He couldn't be sure.
But when he'd defined himself as a genius for so long, built his personal identity around being the cleverest person in the room, what would he have left when it was gone?
So drugs filled the gap for a while, and that was nice, because he didn't have to think about how not clever he was when he was high, because he was high dammit, and any stupidity that happened then was obviously not his fault.
Of course, some people obviously saw it as a damaging habit, with all their infinite wisdom (naming no big brothers, of course) and decided that Sherlock needed something else.
"You don't have to define yourself as something special," Mycroft told him.
Sherlock thought that was funny, the man who was the British government telling him that identity didn't matter, that defining yourself in order to carve a place out in the world didn't matter.
Sherlock ignored him. Mycroft wasn't always right, no matter how often he may have thought so.
So Sherlock searched out other things that he could be the best at, the only one of, the most of.
He tried a few things, none of them working out (he thought he'd made a fantastic criminal, but knew that Mycroft would shoot that idea down before it even got off the ground, but damn, it would be fantastic.) until he realized that perhaps instead of being the one to commit the crimes, he could be the one to solve them.
Not as police, he had no patience for the schooling, he'd suffered through enough of that. (Perhaps he was somewhat of a perfectionist, not wanting to partake in anything unless he knew he could get it right, solve it, be the best at it.) Besides, there'd be too many dull things that he would inevitably fail at because of his lack of interest.
And rules. If he was a police officer, there would be far too many rules, those pesky law things, all designed to keep idiots in their place, and keep geniuses like him from reaching their full potential.
Which simply wouldn't do, because he was looking to excel, not merely achieve.
So he invented his own career, consulting detective, got business cards printed, made his skills into a job, a career.
Sherlock Holmes, consulting detective. The only one in the world.
That was more like it.