An interesting new study in the November, 2008 issue of Personality and Social Psychology Bulletin by Linda Houser-Marko and Kennon Sheldon sheds some light on that question. The point out that there is lots of previous research (much of it by Dan Wegner and Robin Vallacher) that points out that people are able to identify the actions they are carrying out at a variety of different levels of generality. For example, imagine that you are talking on the phone in order to ask your friend whether you can borrow her car. If someone stopped you in the middle of the conversation and asked you what you were doing, you could say "begging for a car," or perhaps "asking a question" or even "speaking into the phone." The first of these is a very general statement of what you are doing. The last of these is a very specific action that is part of the more general action of begging for a car.
When you want to motivate someone to do something, you tell them to Dream Big, and to Reach for the Stars. That is, of course, important advice. It is hard to achieve greatness without ever dreaming of greatness. An important question, though, is how you should go about achieving that greatness after you have dreamed it?