The pinpoint principle is a basic design principle of subject wikis. The design principle is that a user should be able to, with minimal effort in learning the lay of the land of the subject wiki, get an answer to a specific question (of a variable degree of specificity) as quickly as possible. The gold standard is that the person should simply be able to type something in the go/search bar and land on the page that addresses the user's question, and has the right context and setup for further exploration of the topic.
Why the pinpoint principle?
The core reason is that people want quick answers to questions. The longer it takes for a specific question to be answered, the fewer questions a person is likely to ask. The fact that speed can have a decisive impact on the extent to which people are able to explore and learn is not new -- it was the subject of the Velocity Conference where search engine people and other web folk gathered together to discuss the significance of Internet speed.
Another reason is increased accessibility. A large number of textbooks and lecture notes on a wide variety of subjects are available to people learning a subject, yet these are not usually available in a ready-to-use form. Even though long textbooks have table of contents, index, and (in the case of online textbooks) search features, the organization is not fundamentally designed to contain information designed to answer a specific query from start to finish.