Stated otherwise: "Sufficiently advanced requirements are indistinguishable from code".
Abstracted requirements define outcomes. Fine-grained requirements define code.
The customer has given a requirement that states the variable <y> has to be calculated as y= x +1.
However, the code that exists has been implemented such that <y> is calculated as y= x - 1.
y=x-1 is how the current system behaves. However it conflicts with the actual requirement, which is y=x+1.
If the customer would like to describe the ideal behavior of the system, the only way is to translate it into code.
Stated otherwise: "Sufficiently advanced requirements are indistinguishable from code".
Abstracted requirements define outcomes. Fine-grained requirements define code.