The Doctor had always had a companion, usually a human, with him.
The Doctor almost always won every battle he ever partook in.
And with the amount of times he'd preached about the ingenuity of humanity it wasn't too big a stretch to imagine that the two might be related.
But he didn't want just any old human, he didn't want someone who could break and shatter. Unless she was breaking and shattering the Doctor's heart.
So he searches high and low for the perfect human companion.
Should it really have surprised him so much when he found Amelia Pond?