Comment by akoumjian

Broad full text search is incredibly hard to do well. I've had to build, maintain, and improve multiple search systems. The difficulty is largely dependent on the context of the type of search problem you are solving. A lot of complexity depends on your answer to some of these questions:

  - Does the searcher already know the result they are looking for? (If yes, much easier)
  - Are there subjective and objective qualities of the results which should alter the search score, sometimes separate from the text being indexed? (If yes, much harder)
  - What is the quality of the text being indexed? (If end-user provided, this will vary widely)

Ultimately, building good search is often a struggle against providing the best possible results between searcher intent and incomplete document evaluation criteria. People never really think about when a search is working really well, but they definitely know and complain when it's working poorly.