This can often be a difficulty because a user may think that something which has been abstracted away is important. In rhetoric, which is the art of using the spoken or written word for argument, metaphors are used as models. In a metaphor one kind of object is used in place of another. Unlike a simile where an explicit comparison is made in a metaphor the parallel is implicit. The icons used in the various windows interfaces use metaphors to suggest the function of the tools behind the icon.
Users form conceptual models of how a system works based upon their own mental model of the system.
This is why in casual conversation people so often personalize the actions of a computer. The system model of the objects of the system and their relationships The task model, a dynamic model of how the user can interact with the objects in the system to accomplish tasks, Metaphors which help users apply knowledge about the structure of things they already know to the structure of the system and task models. Finding good metaphors is an essential part of the design process. Talk to potential users about how they think about their tasks. Section 8.4 of the OOUI book provides a catalog of metaphors that have been used.