I grew up using the storey system in China and North America. So for a long time, I couldn’t think of any logic behind the European system. See illustration of the two systems below.
I had always thought since it is natural to count from 1, 1st floor must be the most accessible storey, not the one above it. However, it is not until recently when I thought more about it that I discovered that the European system is certainly superior when storeys below ground are involved.
If I walked 2 storeys up from 1st floor, I’d end up on 3rd floor no matter if I’m in Europe or North America. And I can calculate in this way: 1+2=3.
If I walked 2 storeys up from underground 1st floor (or negative 1st floor), I’d end up on 1st floor in Europe. And I can still calculate it in the same way as above: -1+2=1 . In North America, I’d end up on 2nd floor. But to calculate it, I’d have to add 1 to the sum to get to the right answer, in other words -1+2+1=2. Similarly when calculating the number of storeys between a floor below the ground and a floor above the ground in North America, one has to subtract 1 from the difference. All this adding-or-subtracting-one-business is caused by the lack of 0th floor in the North American storey system.
The non-existence of the 0th floor (ground floor) in the North American storey system can be compared to the non-existence of year 0 in our commonly used calendar system (the Anno Domini system). When calculating the number of years between a B.C. year and a A.D. year, we have to subtract 1 from the difference between the years. For example, the number of years from 10 B.C. (year -10) to 10 A.D. (year 10) is calculated as 10-(-10)-1=19.