This is usually because the user has a broad topic for a research project or paper, thus will need to narrow their topic. In this case, show the user various results from the catalog or one of the broad databases to help find a topic that works.
The user may know his/her topic, but doesn't realize the other sources available. For example, a student found a book about life on planet Mars, but may be unaware that there is a journal and encyclopedia published about planet Mars.
Offer to look at the class syllabus or assignment if a student shows hesitation about revealing the topic. The student can then say it is not for a class. You can then show a non-specific search to demonstrate using Discover.
Follow up with showing the appointment link giving the student a chance to privately meet and discuss the topic.
There may be some kind of communication barrier. Try paraphrasing what the user says back to possibly pinpoint the misunderstanding. Don't be afraid to politely ask them to repeat or spell the word if it is a communication problem.