The main liability with existing collaborative filtering systems was that it required the collection of preferences. In order to be reliable, most systems needed a large number of people (typically thousands) to express their preferences about a relatively large number of options (typically dozens).However, the system only became useful after a critical mass of opinions had been collected. Users were not motivated to express detailed preferences in the beginning stages (e.g., by rating dozens of book titles on a 10 point scale), when the system could yet help them.