You might miss relevant documents. Try synonyms and variations on words Try with another search engine. Your search produces too many results Try to be more specific. Identify common words that are important to your search. Try to think of words that uniquely identify what you're looking for.
Some words are of little value, because they identify lots of documents.
The most distinctive a word, the more useful it will be for sharpening your search. No answer, Timed out, Too busy These are the most common type of problems you will get. The server you are trying to access may be too busy or temporarily down. Wait until a less busier time of the day. Avoid prime time hours.