When Mycroft was seven or eight years old, he fell out of a tree he was climbing and broke his wrist. In the end, it wasn't the injury that Mycroft remembered, for that was quickly remedied with a cast and some mild painkillers. What he remembers most about the day is what his mother said to him while on the way to the hospital.
He'd been crying softly in the back seat. Mycroft didn't often cry, but his wrist hurt terribly, and it was hard to avoid moving it. After a few minutes of this, his mother spoke from the front seat.
"Now, Mycroft. You're far too old to be crying like that."
Mycroft had only sniffled, embarrassed.
"You're a big brother, now, remember? You have to give a good example for Sherlock. I know it may not seem important now, but there might come a day when Sherlock needs you to be strong."
Mycroft had nodded, taking the words to heart. He wanted to be a good big brother, after all.
When Sherlock was very young, being strong simply meant putting on a brave face. Whenever he scraped a knee, or if the two got lost exploring. He'd be the one to keep calm.
But as both boys grew older, things changed. Granted, neither had ever been very emotional children, but they'd always seemed to understand each other. Now, as Mycroft's intelligence grew, so did his ambitions. He needed to work, to be serious. He didn't have time for childish games anymore.
By the time he realized Sherlock and he were drifting apart, the ambition had taken over. As Sherlock began to resent Mycroft, Mycroft tried to justify his actions to himself. It was for the best, wasn't it? Wasn't this staying strong? Mycroft was going places. Sherlock could learn from example and follow him.
But he didn't.
Sherlock was six when he first told Mycroft he hated him.
And as Sherlock continued to grow, skipping school, failing classes, and experimenting with drugs, he spiraled farther and farther away from the path that Mycroft walked.
Mycroft didn't know what to do with him.
By the time both of them were grown, there was a rift between them. And there was nothing Mycroft could do to fix it.
It hurt, but Mycroft would never show that.
So he tried to help from afar, tried to watch over Sherlock from a distance, because Sherlock would never accept the help outright. It seemed to work just fine that way.
That is, until James Moriarty.
Late at night, three days after his little brother's death, Mycroft sat in his home, thinking about his broken wrist.
There would come a day, his mother had said, when Sherlock would need him to be strong.
He'd been preparing for that day his whole life.
He'd missed it.
When Moriarty tempted him, when Sherlock needed him to be strong more than ever before, he'd made the weakest decision he'd ever made.
And so, sitting alone, he cried that night for the first time since he was the little boy with the broken wrist.
He had no one left to be strong for.