http://en.wikipedia.org/wiki/Principle_of_least_effort

The principle of least effort is a broad theory that covers diverse fields from evolutionary biology to webpage design. It postulates that animals, people, even well designed machines will naturally choose the path of least resistance or "effort". It is closely related to many other similar principles: see Principle of least action or other articles listed below. This is perhaps best known or at least documented among researchers in the field of library and information science. Their principle states that an information seeking client will tend to use the most convenient search method, in the least exacting mode available. Information seeking behavior stops as soon as minimally acceptable results are found. This theory holds true regardless of the user's proficiency as a searcher, or their level of subject expertise. Also this theory takes into account the user’s previous information seeking experience. The user will use the tools that are most familiar and easy to use that find results. The principle of least effort is known as a “deterministic description of human behavior.”[1] The principle of least effort applies not only in the library context, but also to any information seeking activity. For example, one might consult a generalist co-worker down the hall rather than a specialist in another building, so long as the generalist's answers were within the threshold of acceptability.