John had always known that you couldn't save everyone.
He knew it before Sherlock, before murder victims and lost loved ones. Before crime scenes where women etched the name of their unborn daughter with their nails into the floor as they lay dying. Before an old woman mentioned a soft voice and that was the last thing she said before there being a disconnected call. Before children strapped to bombs begged on the phone for someone to come save them. Before flights of the dead and women who would do anything for their own protection. Before men would fly off roofs when confronted with a final problem.
He knew it before he went to Afghanistan, where bullets ripped flesh and lives apart. Where lives ended in the blink of an eye and a bullet that left blood on the sand. Where children took care of themselves and their siblings because parents were gone. Where a good day was one where John could save a leg, save a life, or at least allow one to end in less pain thanks to a clear liquid injected into burning veins. Before he got shot, ending his tour and his career in the army, if not as a doctor. He knew it before he was sent home to a world that could not possibly compete with the adrenaline fuelled brightness that was life and death battles.
John knew it before medical school, where he took courses in end of life care and how to break the news to families. Before he had to actually do it, on his first patient that died, a sixty five year old woman who'd had a stroke and he had to tell her husband, the first man John had ever seen cry.
John knew it before that psych rotation, when he met the teenager just blossoming to a young woman, in the hospital because she'd slit her wrists too far this time, and almost didn't make it. John listened to her pain, while she explained why she carved her skin into patterns that made her feel better, about her abusive father who didn't hurt her, but instead used her sister, and she hated that. John wanted to make everything better for her, but he couldn't fix it when she came back into A&E three days after being discharged, having been found hung in her bedroom. John knew then that you couldn't save everyone.
He knew it before that, on his NICU rotation when a baby was brought in, severe inter-cranial haemorrhaging, by a sobbing and unstable father who said, through the tears, that she just wouldn't stop crying and all he wanted was for her to stop, with the mother who'd just had a nap, exhausted after giving birth to her first child, only to wake up to find her life in pieces. She had a horrible emptiness to her that John hated. He couldn't save her either, even if she was right in front of him.
He knew it before his paediatrics rotation, when he watched a boy die of leukaemia and a girl die from a weakened heart. He couldn't do anything to help them, save for pulling a new heart and some bone marrow out of a magic bag, but it was still awful to watch it happen.
He knew it before he was a child and the girl who lived down the block was hit by a car. His mother held him and Harry, kept them from going to see, but she couldn't hide the screech of tires and the lasting memory of blood on concrete that was made on a young boys brain. But mostly, she couldn't hide the wailing of a mother who hugged her child in her arms, broken and bleeding, and watched as the light left his eyes.
John knew it even before that, knew it like he knew his name, like it was etched into his DNA, like someone had been whispering it in his ear every moment since birth. You can't save everyone. Of course, that didn't mean he wouldn't try. He just never thought it would apply to Sherlock.
So John damn well knew that you couldn't save everyone when Sherlock stood on that rooftop and he watched in slow motion as he fell to the unforgiving ground. He knew that you couldn't save everyone. he'd accepted that fact, lived with it for his whole life, perhaps even longer. But that didn't mean he had to like it. That didn't mean he couldn't try.