Books
I get all my ideas from a mail order company in Indianapolis. Although I'm not prepared to give you their name.
— Douglas Adams · Chat, June 17, 1998

Behind the line May contain spoilers.
Our reading
An editorial interpretation.
Adams describes ideas as goods obtained from a business, then withholds the detail that would make the explanation useful. The specific city gives the claim a practical shape while the missing company name keeps it inaccessible. An apparent disclosure therefore manages to reveal almost nothing another person could follow.
Context reviewed