Before John, there’d been headphones.
In-ear headphones, black ones, blocking his auditory canal from at least part of the external noise.
(The internal noise had been enough, had been more than enough.)
Sherlock had worn them whenever he was outdoors as long as he wasn’t on a case, because cases had their own way of shutting off the endless shatter of everyday life all around him, and cases required him to be alert, to use all his senses to gather useful information.
That’s the crux, really.
Never knowing what’s important and what is not, Sherlock had erred on the side of safety, dismissing as much input as he could as ‘nonsense’, not wanting to clutter his mind and run the risk of not having the necessary space and focus for what really mattered.
So there’d been the headphones.
And then there’d been John.
John is nothing like modern composers or the subdued almost-silence of just using his in-ears without even bothering to put any music on. That had been means to an end, just something to drown out something else.
With John, it’s more about having a focus. A single fixed point in the soundscape of busy London streets and endless customer announcements in stores. John is more about not wanting to miss out, even when neither of them had said a word in twenty minutes.
Now, the headphones have become a tangle in the pocket of Sherlock’s Belstaff.
They’re still being used - John isn’t always with him when he goes out - but they’re no longer his constant companion, the one thing he relies on as a filter between him and the noise floor of things that wants to eat away at his brain.
The headphones hadn’t always been enough, and John isn’t always enough.
It’s a bit of a nervous habit, his fingers playing with the cord and the in-ear pieces in his pockets at all times, but especially so during the times when Sherlock wishes John hadn’t been there so he could just plug in his headphones and make the elevator music get dulled down to a tolerant level, or drowning out the screaming toddler by the bus stop.
He could, of course, still use his headphones even if John was with him. John might find it irritating to be so obviously shut out, but John is used to be ignored at times, even without the visible barrier of headphones. It’s just that Sherlock finds that he might want to endure certain things when John is there. It’s bearable, because he has something of a focus, something of slight interest in the outside world.
It had been unexpected, finding knots on the cords of his headphones.
But then John seems to be the cause and solution to many different kinds of tangles.
Finding the loose end and untangling Sherlock’s spinning thoughts with a single sentence at the end of cases.
Making Sherlock leave his headphones unused long enough to grow to become a tangle in his coat pocket.
Tangling Sherlock’s intestines and his unreliable, traitorous emotions with a single, ambiguous glance.
Before John, Sherlock hadn’t known the level of which he was willing to allow him himself to become entangled.
After a few months, Sherlock starts leaving his headphones in his pocket simply because sometimes he needs the outside clatter to drown out the noise John is causing inside his head.