I think the concept you are looking for is Tacit Knowledge (aslo known as implicit knowledge).
The main reason that users cannot articulate what they want, is that they do not have any conscious access to the knowledge they have acquired over the many years of practice. That’s why an iterative process is needed to bring the tacit knowledge on users awareness, so that they can articulate it.
Definition from wikipedia :
Tacit knowledge (as opposed to formal, codified or explicit knowledge)
is the kind of knowledge that is difficult to transfer to another
person by means of writing it down or verbalizing it. For example,
stating to someone that London is in the United Kingdom is a piece of
explicit knowledge that can be written down, transmitted, and
understood by a recipient. However, the ability to speak a language,
knead dough, use algebra, or design and use complex equipment
requires all sorts of knowledge that is not always known explicitly,
even by expert practitioners, and which is difficult or impossible to
explicitly transfer to other users.