Disclaimer: I don't own Doctor Who.
In the great big universe there are some parallels. Most of them go unnoticed. One of them is that the Medusa Cascade looks startlingly like the moldy stain under Sylvia Noble's fridge. Another one is the fact that there is an completely normal crack on the stairs in Rose's old apartment. It looked frighteningly like the crack in time, but it was normal and it was just one of those unnatural parallels.
Another one is Donna. Donna Noble was a feisty ginger with a fiery temper. She was the Doctor's best mate.
Another one is Amy. Amelia Pond was a feisty ginger with (if she got a mind to it) a fiery temper. She was the Doctor's best mate.
Now some might say that 'that's not true, they're not the same- there's quite few differences.'
They are different, but there are still some unnatural parallels.
Donna Noble, the girl who forgot
["Doctor! I don't want to forget! Doctor! No! Please, don't-!"]
And
Amelia Pond, the girl who remembered.
["Raggedy Man, I remember you and you're late for my wedding!"]
There are some unnatural parallels in the world, some come right after each other or end as the other begins- but most of them slink by unnoticed by the world.