Time isn't often linear for the Doctor. It's very rare that he will meet someone in order and have that pattern continue for the rest of their life.

Linear time is boring anyway, always going forward and never going backwards. Always knowing what was coming next, never any mystery to it. That's what he loved about time travel, it wasn't straight but it wasn't circular either, it was all over the place. He never knew where he was going to end up next, who he was going to see next, what was going to happen. He lives for it.

Sometimes the stars will align and he will meet someone throughout his lives in order. Take Brigadier Lethbridge-Stewart for example. They met in his Second body and continued to meet all through until his Eighth, each time the Brigadier looked older, never younger, and The Doctor in a new body after several meetings. Only during that business with The Death Zone did he and the Brigadier not meet in linear time what with his previous selves having been there.

He was grateful for the linear times, there wasn't the mess of trying to figure out what adventures they had gone through, trying to guess what crucial information they couldn't reveal to each other, having to walk on eggshells until they figured it out.

But then there were times he met people out of order, which he didn't mind when they hadn't met often. Not many adventures to compare, less of a chance of risking the timelines and blowing a hole in space.

Until he met Darzil Carlisle, the man who had single handedly brought peace to 36 planets. 36 worlds. Prevented the deaths of billions of people. All within his short life. His young life. He admired the man from afar. Placed him upon the pedestal and admired his integrity, courage, and intelligence.

They do say never meet your heroes.

And he should have listened.

Oh Rassilon he should have listened.

He found a man that wasn't quite so charismatic as he'd thought, fumbling over his words and struggling to put coherent sentences together. It wasn't very impressive, it wasn't the Darzil he'd built up in his mind. He wasn't a very good speaker, not when he didn't have the words written out for him.

That's when he found out that it wasn't Darzil who single handedly saved 36 worlds, he had someone with him. Someone feeding him lines, someone telling him what to say, what to do, claiming credit for someone else's work.

"Someone who never got older, someone who matches your description right down to that celery stalk on your lapel."

Of course, it was his words. His speeches that Darzil was using. Time had dictated what he needed to do and where he was going to be in this lifetime. He hated it. The only thing it didn't dictate was when. Would it be like next week? Next month? He could go on four different adventures before encountering Darzil again.

And to top it off, because the universe was just that cruel sometimes, Darzil had sacrificed himself for The Doctor. So that he could live, never mind that The Doctor would regenerate and couldn't quite die just yet, not while both his hearts were still ticking.

"You got to say goodbye to me, but I didn't get to say goodbye to you. The real you, I mean. And now I never will, he doesn't exist yet. So here I am dying, and I'm stuck with you."

And didn't that just tear at his hearts. He deprived a man of his goodbye with his best friend. A man who was him, but not quite. To Darzil, he was just a stranger, like the many that surround him on a daily bases. Saying goodbye to this version meant nothing compared to the goodbye he could have had with the older him. The one who knew Darzil and had a history with him.

At least he had a friendship to look forward to, a very special and important friendship. That was something time couldn't take away from him. A friendship with the wonderful man. He had something to look forward to, something to keep him going. He was going to have decades with this man, stopping wars, saving lives, and enjoying their time with each other.

For as much as he found linear time boring, sometimes he found he wished for it. More than anything else.