The most important thing I can add from my own observations is this: Knowing it started from unremarkable circumstances should be a comfort to us all. Because it proves that you don't need much to change the entire world for the better. You can start with the most ordinary ingridients. You can start with the world you've got.
And then, every time I didn't see her, there was a fall involved. I thought about dancing on the fifth-floor ledge outside out apartment. Every train she wasn't on felt something like hitting the pavement from five floors up. So maybe my father was right about that. Maybe happiness and excitement really are dangerous things.