So Far, So Good

What is the origin of the term "So far, so good" ?

A man jumped from the 10th story and is falling to the ground. A woman at the 4th floor sees him from her window and asks, "Hey, how's it going?". The man replies "So far, so good."

So now you all know what it means when your colleague tells you "so far, so good" when you ask him how his day is going.