How does a researcher know if they have chosen a topic that is too narrow?

Responses

They cannot make connections between the facts.
They cannot make connections between the facts. - no response given

They cannot find much information on the topic.
They cannot find much information on the topic. - no response given

They cannot distinguish between the facts and opinions on the topic.
They cannot distinguish between the facts and opinions on the topic. - no response given

They cannot locate living subjects to interview.

They cannot locate living subjects to interview. - no response given