Everyone kept telling me I would love Donna Noble by the end of Dr Who season 4.
That hasn't happened yet, not exactly, but I do appreciate her. And considering how much I... we'll say "disliked"... Donna's know-it-all attitude when I began, that's saying something. (sorry Jessie)
Near the end of the season, the writers throw in what I have affectionally called the "It's a Wonderful Life" episode, in which we see what the Doctor's life, or, more accurately, the Earth's life, would have been like, had Donna Noble not met the Doctor. A simple decision to turn right instead of left, that's all it takes, and the world's a completely different place. I can say that much without giving away any spoilers.
For me, this was a turning point. I now understand Donna's complex involvement in the Doctor's story, how she became, quite literally, the most important person in the world.
And it makes me wonder about the people passing by me every day. About their choices. About my own. About the seemingly simple, presumably inconsequential decisions to turn left or right.