Prompt: Sherlock generally avoids touching people because when he does he can see flashes of that person's future. Most of the time it is quite short term things like what people will say next. However no matter what he sees he cannot alter the future, he knows because he has tried before.
The worst thing he could have ever done was shake John Watson's hand.
Most of the time it was tiny, miniscule things that were unimportant, like the sentence they would say next, or what they planned to eat for lunch. Sometimes, if they were incredibly organized, it would be what they were going to wear the next day, or their plans for the weekend.
But when he touched John's hand, his future was laid out in front of him. And that was something Sherlock didn't ever want to have to see.
He knew from experience, that once he saw something, it happened. He could not change it, no matter how hard he tried. He didn't know if that was because he'd seen it that it had to happen, or if it was just meant to be. It wasn't like he could test with control groups, because human behaviour was anything but predictable. And the only way he could know what was to happen was to see it, which ruined the whole point.
So whether it was the act of seeing what was to be that fixed it, or whether fate ruled the universe, Sherlock could not determine.
He favoured the former idea, not overly fond of the concept of no free will, that everything was going to happen any way, no matter what he did.
He didn't like the idea of being controlled.
So he stuck with the concept that by seeing it, he made it happen, and avoided skin contact whenever possible, wearing gloves, acting aloof, and generally having no friends.
It gave him an air of being antisocial and cold, but honestly, he preferred that to what he could have been, a bearer of deaths and heartache, one moment at a time.
When he shook John Watson's hand, against his better judgement, he could see everything.
Not in depth, because he let go of John's hand like he was burning him, but he saw the vague outline of the path he would take. Saw the twists and turns his life would take, like looking over a board game before starting.
He only saw the next little bit in detail, John moving into Sherlock's flat with him, a chase, a cabbie.
A death. (There always seemed to be a death. At least this time, he hoped it would be somewhat deserved.)
So he set the wheels in motion that needed to be rolling, and took off, his heart racing at the danger of what this man could mean.
And what Sherlock's connection with him might cause.