Dennis G. Jerz | Associate Professor of English — New Media Journalism, Seton Hill University | jerz.setonhill.edu
The running you do in a 100-yard dash, an obstacle course, a 5k charity walk-a-thon, a marathon, and when you are being chased by a bear all serve different functions, and the amount of distance we need to cover is only one of the ways these modes of running differ.
Likewise, the writing you do when you compose a text message to your angry significant other, a timed paragraph on a midterm exam, a 1-2 page personal essay, a 3-page persuasive essay, and a 10-page research paper is very different, and the number of pages you are expected to produce is only one way that these modes of writing differ.
You can’t expect yourself to just keep sprinting longer in order to finish a run that requires endurance, and you can’t just produce more personal opinion in order to finish out a paper that requires research.
The main function of running from a bear is to make you a more attractive target for a mauling. (I mean, this works with the metaphor. Knowing when not to write anything at all is a valuable skill.)