As the great ads man Rory Sutherland once said:
1x7 is not equal to 7x1
How is this possible? Because of human perception.
Economists and mathematicians create constructs that sometimes don't mesh well with the actual truth of reality.
The fact is that 1x7 is not equal to 7x1 because it doesn't factor in that we are human beings.
1 customer buying 7 things is different from;
7 customers buying 1 thing.
That when I pay for my $5 ice coffee in cash - it feels way more expensive then when I pay for it on my contactless rewards card. However, an economist would look at this as a $5 transaction no matter what.
Remember that not only do we need to look at the world through the lens of an economist or mathematician but we also have to look at it through the lens of human psychology to get more of a full picture.