When we teach onsite technical, business, and scientific writing courses, we always talk about purpose, and not just about the writer's purpose, although that's of utmost importance. What writers need to understand is the reader(s)' purpose, or why the reader is reading. In many cases, of course, readers "have" to read the document, or part of the document; however, this doesn't mean that readers don't have a purpose for reading and/or that writers shouldn't think carefully and critically about that purpose.
Too often, writers forget, or simply don't consider, that the reader has a real purpose for reading. Superficially, this purpose may be simply to get information; however, as I suggested in an earlier blog, this purpose may also be to assess the writer's ability to think, to organize, and to attack a problem. While the reader may not necessarily be cognizant of this assessment, nevertheless, this kind of assessment goes hand-in-hand with whatever other purpose the reader may have.
Writers also need to think carefully about their purpose, or what they wish to acheive via the document. Certainly, they should strive to write a document that conveys their ability to think critically, organize, and attack a problem; however, they should also think carefully about the outcome they hope for. That is, what action they want their readers to take after reading. This action could, of course, be that the reader thinks positively about the writer, but could also be a physical action, such as reading the document more fully, passing the document to someone else to read, or any of a number of such actions. The point is that writers who fail to consider the desired outcome, or the action of their readers, will, in all likelihood, write a document that portray the writer in the way that she desires and/or fails to achieve its purpose.