As we all know, the Duke of York had 10,000 men. And when they were only half way up, they were neither up nor down. Surely zero, coming at the junction of positive and negative numbers is also neither up nor down (neither positive nor negative, if you prefer)?
Zero is an interesting concept and one that simply did not exist in mathematics for a very long time. Even in Shakespeare’s time, the notion of nothingness was shied away from as it suggested an absence of everything, including God. And they couldn’t have that!