Generally we think about users as the people for whom a design is made. Designers build systems intended to be used by users.
But it might make more sense to see users as an intrinsic part of a design. Designers build systems composed of non-human and human elements. (The designed artifact is only part of the system a designer develops.)
This might make it easier for designers to explain to engineers why it is necessary to include users in the design process — users are one of the most fundamental materials from which the system is made. What competent engineer would build something without first knowing the materials thoroughly? It would also help designers extend the scope of design to often neglected organizational considerations (governance, support, editorial process, etc.) that determine the success of the design.
Engineered systems are composed of objective materials. Designed systems are composed of both objective and subjective materials. Both must understood their materials to build good functional stuff.