Terrible Twos

I was familiar with most of the ideas presented in Greg Notess' article after completing Intro to Information Science and Technology last semester, but the concept of the "Long Tail" was new to me. Although it is important for libraries to provide the most popular materials , this theory suggests that the greatest portion of circulation may come through the varied and widespread use of the the more obscure items. This seems to contradict the idea of the Pareto Principle which I references in a previous post discussing Lee Rainie's lecture on "The Networked Librarian." Maybe there is no pattern that applies to all situations after all, - be it Long Tail or Pareto - but some other variable(s) that leads certain systems to prefer one result over another.