Everyone thinks it's seeing the future. It's really not.
He doesn't see the future. He sees the likelihood of each individual event occurring. That was what he saw. Nothing more.
Besides, even if something was 99% sure, if Sherlock stuck around long enough for it to happen a hundred times, he would eventually be wrong once.
That's just the way numbers work.
It's how he met John.
As Sherlock saw it, there was only ever a .001% chance that he would meet someone who would actually like him. So in order for the math to work, he would need to meet 99999 people who did not like him to meet 1 who did.
Now, Sherlock wasn't sure he'd met 99999 people so far (no, he doesn't keep count, why would he keep count?), but if he did, he'd bet that they all disliked him. But here was John and, against all odds, he actually seemed to genuinely like Sherlock. For such a clever man, Sherlock couldn't figure out why. It baffled him. Not to mention that John didn't make sense numerically, because his odds always seemed to add up to 104% or 97%. Sherlock was rather unsettled by this. Percentages were to equal 100. That was that.
Numbers had always been a great comfort to Sherlock. Number were predictable. They made sense. They were a constant in his life. He could always count on them.
That was, until John came along.
Because after John, there was more than numbers. More than odds, statistics, probabilities. There were unquantifiable elements that Sherlock had never had to put up with before. The inscrutinizable. So many things that Sherlock had always been able to block out because they simply didn't matter.
But now, there was John. John Watson, a man of fuzzy grey areas and jumpers alike.
A man that could not be captured in numbers alone, or in percentages, or in likelihoods or predictions. He was a variable. And even though it was refreshing, it absolutely terrified Sherlock.
John bought milk, even though Sherlock was the one who used most of it in his experiments. (He used 76% of it.) But John likes milk in his tea. (As do 48% of people.) John shops at Tesco's to get milk (99% of people have been to one) but refuses to use the chip and pin machines (12% of people). Of course, he was pretty sure John was the only one who'd had a row with one of them. (Need more data.)
John wasn't gay. (Sherlock was 93% sure.) Neither was Sherlock. (Again, 93% sure.) It was all just fine. (Actually, it was, odds being 78% that it was true.)
John tolerated his violin playing, even in the early (late?) hours of the morning, and even claimed to like some of it. (Hard to tell if he was lying. Odds are 84% he's telling the truth.)
He did seem a bit perturbed by the contents of the fridge occasionally, and threatened to throw them out, but it never happened. (Just as Sherlock knew it would, only 6% chance.)
John even tolerated Sherlock pushing his girlfriends away. (90% of them within 2 months even.)
He'd just said to Mike that morning about needing a flatmate, so it was odd when he returned, just after lunch with Dr John Watson, recently invalided home from Afghanistan. Limping, psychosomatic (90%) brother who's an alcoholic he doesn't get on with (87%) and rather desperate (96% he'd come live with him, 32% he'd stay more than a week.)
And he even came with him on cases. What more could Sherlock ask for? (The removal of Anderson, 4%, more murders, 1%, also not decent.)
But this would be acceptable for now.
He was pretty sure he had the right pill. (82%) He never saw the shot coming. (0.003%) He was terrified when he realized it was John (99.6%) and thought that even Lestrade was clever enough to figure that one out (78%) but was overly relieved when he said nothing, and doubted he would any time soon, if ever (3%).
He was pretty sure John would stay after that. (97.3%)
He didn't think she would die. (8%)
He didn't think he would be strangled. (16%)
He didn't think they would take John, thinking he was him.(0.9%) Rather stupid really. (IQ95, 76%).
Of course the cases were linked. (99%) Of course they were just a distraction. (94%)
No, this, this was what he was really up to. Moriarty. His fan. (91%)
He knew he'd come. (96%) Not like him to miss a challenge. (1.5%)
He'd never considered that John had been Moriarty. So when he stepped out at the pool, Sherlock blanked. (INSUFFICIENT DATA).
It could be true. John was so unquantifiable that it could be true and he just didn't see it coming. John is grey areas and fuzziness and jumpers and milk and girlfriends he can't keep and he used product in his hair and he is so changeable and oh god it could be him I knew that no one could actually tolerate me and he was just pretending it was all an act act act...
But then John spoke and they weren't his words. (93% probability of not being his.)
John pulled open his jacket and it was not his bomb. (97% probability of not being his.)
But then Jim from IT stepped out and the world make sense, odds crashing into place, breaking his concentration and hurting his mind.
One hundred fucking percent.
And then it was panic, panic, panic. Because none of the situations were good. Odds of survival were minimal. (11% at best.) Even taking into consideration John's fuzzy grey factor. (Give or take 7%. 18% survival at best.)
And that one was the worst. Riskiest.
But he never could have seen coming what came. Really. (0.0007%) He just didn't look for that sort of thing. So... insignificant.
He was just thankful it did.
Probability of going to palace, 99.3%. Probability they'd actually let him go in a bed sheet, 17%. Oddly enough, it happened.
They were actually going to shoot John. (89%) Not a risk he was willing to take.
He wasn't positive he had the right numbers. (Only about 69%). But it was better than nothing.
And, thank god, it worked.
He didn't see the next bit coming though. Another one of those things he didn't look for. (0.004%) Much too insignificant for him to bother with all of those situations. Even as he faded out of consciousness, he had a hard time believing it. (Likely from the drug though. Thinking is hard when your brain is failing.) Even when he woke up, foggy and dulled, hours later, he had problems grasping that it actually happened.
But then there was the phone, and it all became real. (91%)
Last chance, last chance. Odds that it would work? Not so good. (38%)
But better than nothing.
And sure enough, SHER.
Odds that sentiment would be her downfall? (85%)
[Odds that he suspected it would be his? 0.009% And yet, of course, because John was involved and John had his damn fuzzy numbers and jumpers and ruined every decision Sherlock had to make.]
He couldn't find them. John was so damned unquantifiable and that leached into everything he did.
And even Henry didn't appear promising. (76% chance of being less than a 7, and therefore, not worth leaving the flat over.)
But it became a 9 with those words thrown out at random. "They were the footprints of a gigantic hound." Then it was interesting. (69% of it being above a 7.)
More deadly than a rabbit. Oh John, you are clever. (83% of animals in fact.)
The hound wasn't real. Couldn't be. (0.02%) (Note to self: work on a better way of categorizing those very unlikely percentages. They'd been coming to bite him recently. )
It had to be in the sugar. (79%) There wasn't anything else.
Timing? Oh. Must be a bit not good. (92% likelihood the answer to that question was a yes. )
Odds that Moriarty would get off. (6%. Fixed, obviously.)
Odds that Moriarty would come see him. (99%)
Odds that he would be blamed. (68%) That they would believe he actually did this. (67%)
Odds that he would be arrested, (78%) by Lestrade no less. (71%)
He suspected the plan the minute he left the reporter's house. It was gut wrenchingly likely. (89%)
He knew the likelihood that he would have to jump when he got up on that roof. (98%) Knew that he'd be able to do it, to pull it off (97.2%) but knew all the hurt it would cause. (Hurt cannot be measured.)
He knew how true it was what Moriarty was saying. (99.98%)
Oh god he never expected that one coming. Not his death. (0.0001%) (Did he not look at those minor percentages?) Not likely he could survive that. Gunshot to the head at close range? (0.0006% chance of survival.) Still, horrifying.
He knew that John would believe his death (97%) but not his lies (42%).
He knew how likely it was that John would hurt him when he came back (79%) or cry (73%) and he wasn't sure which was worse. Doing both, he supposed (27%).
(If he came back. Stop thinking about it like that. 50% and that's all that mattered.)
How many people would actually know and believe the truth. (0.5%, but that included John, and as Sherlock had noted before, John was damn near unquantifiable.)
The odds he would return to John and apologize for breaking him?
One hundred percent.
The odds that he felt terrible for having done this to John?
There are no odds; it's a fact.