Pull quote: "We want to explain why each and every result is in that set. We want to be sure we get 'the pure drop'. This is an essential difference between librarians and the clients they serve. Students do not appear bothered if there are a few irrelevant results - as long as they get more relevant ones than not. They effectively 'bleep' over them and move on. Furthermore, for most students and public library users, the level of satisficing is lower than for librarians and some expert searchers. These attributes may explain why our users (and many front-line reference librarians) love these Discovery services so much more than expert reference and research librarians."