Sometimes, the story is as good as the moral. Sometimes, the journey is as good as the destination. So in Information Retrieval, why are we too often satisfied with producing results, but not with explaining how the results were arrived at?
Daniel Tunkelang talks a lot about the need for transparency in search, in being able to give the user enough understanding and control over the results produced, so that the user can engage the search engine in a dialogue and instruct it to the point that results improve. Only with transparency can the user truly engage in Exploratory Search.
I would like to suggest a name for this goal of transparency: Explanatory Search. If the search engine can explain to the user why certain results were retrieved, then the user has the best chance of explaining back to the engine a refined description of his or her information need. This can only make the user experience better. Exploratory Search requires Explanatory Search.