Sorry. A board game and one of the Doctor's favorite words. Well, not really a favorite, but he did seem to use it a lot. He'd looked up the rules once and it sounded easy enough. He'd never gotten around to actually buying the game, but he still hoped that maybe he'd run into someone one day and they'd offer a round. But it still seemed unlikely. When he was running, usually other people were too instead of sitting down and playing board games.
Himself. That's who he used to apologize to the most when it was just him and the stars and the planets and nothing else. That's when he was selfish and alone, like an ugly oyster hoping to have a pearl inside, but knowing it was empty. When he wasn't so alone anymore, he ran around the universe with his companions in tow, creating messes in all his excitement. Some of his companions saw it all as some beautiful part of the universe, not a result of him pushing the wrong button. But some of them would watch his finger slip and they'd know it was a tragedy, not a treasure. They were the ones who held open his eyes when he tried to close them so he could see what he'd done. It didn't matter how blurry the images became over time. It mattered that his eyes still wandered over them, taking it all in and if not acknowledging, then at least knowing that this was his fault.
He'd held whole worlds in his hands and let them slip through his fingers, leaving the destruction behind with a whisper: "I'm so sorry." That's what was left to console the unlived lives and the centuries of creating to get to a few seconds, minutes, hours, days, weeks, months, years, centuries, eternities ago when everything became nothing for those people. The guilt stays though, to remind him of what he's done. Even when everything bleeds together, crossing over the years to become one mess of his life. Even when he can't remember what year it was that day or who the people were, or how many there were, the guilt stays. Even when the memories come together as hands with fingers, fingers clawing at his throat and choking him, he's learned that the past doesn't die before you.
The Doctor plays a dangerous game. It's not that simple, but he's the only one who knows how to play and win and there's only one thing he can offer to the ones who lose and those who have lost and who will lose tomorrow and the next day and the next day and the next: sorry.