Many people have difficulty with the concept of zero.
In fact, it has only really been used as a number for the last 1500 years or so. Before this time it seems that zero was simply not that important. At the end of the day, a herd of no camels is not worth much. Once you start using zero as a number then you can easily get into difficulty. In a previous issue of PASS Maths we were asked what infinity multiplied by zero was.