I find it interesting that, in order to best visualize the needs of a user group, we must reduce that group down to a single person, quite literally a face. It is fascinating that it is easier to focus on the necessary qualities of a usable service when those necessities are applied to a single person rather than as a whole. Apparently, it is harder to hear “8 out of 10 people would like this feature” as opposed to “Bill would prefer that feature.” What does this say about the psychology of making users happier.
I think it is easier help one (albeit fictional) person than a group of people because we tend to ascribe a sense of emotion to that character. It is easier to create an attachment with a persona and want to impress them. It is much harder to envision the needs of a faceless mass of users. Typically, in social sciences, having a persona refers to putting on an act; in the field of information architecture, the persona is just a reflection of many people. In this way, a persona is an essential step in determining the usability of a service.