This is a kind of abstract question regarding the mechanisms and logic of mathematics.
First, let me try to explain what I tried to convey with the topic title.
Let's say I have a value that gets decreased to a lower one, and I want to calculate the percentage difference, like for example 13 goes down to 8.
13 - 8 = 5
So now I would divide the the difference of 5 to the original value of 13, which is what the topic is about.
5 / 13 = 0.3846
And then of course I'd multiply the 0.3846 by 100 to get the proper percentage difference between 13 and 8.
0.3846 * 100 = 38.46
At which point I know the percentage difference is 38.46.
But the part that really I don't understand, is that there must be a logical reason for why it makes sense to divide the difference of 5 to the original value of 13. I can understand we do it because it works, but I don't understand why exactly it works.
I hope this question makes sense, basically I'm trying to say that on an intuitive level or a logical reasoning level, I can't seem to understand why the difference is split to the original value, other than "it works because reasons".