Our perceptive equipment lags behind the conceptual skills that we as humans take for granted. As a consequence, linguistic explanations of concepts or feelings are represented by a limited medium. We often can’t provide a thorough linguistic representation of a concept or perceptual judgement to ourselves or to others. As a result, we frequently speak in metaphorical terms to describe feelings and concepts. If it is hard enough to express our own knowledge and thoughts linguistically, it is even harder to express the knowledge of others, especially in written documents.
Brian Marick has an article on Tacit Knowledge that underscores the underdetermination of project documents. The documents are an expression of the ideas and knowledge of experts, but in and of themselves do not provide the complete picture. I particularly liked the paragraph where he describes collaborating to gain tacit knowledge, and looking at a requirements document:
…as a tool for aligning the unexpressed wishes of the experts with the emerging abilities of the product