This is great advice about world-building. You do need to make sure that you - the writer - knows every detail of that world though. Even if you don't communicate details to the reader, your knowledge, or lack of knowledge, will be detected by the reader...
Unsolicited writing advice, no. 36571:
World-buiding doesn't mean describing everything. You can do more with a local fruit, a saying or a custom than you can with a dozen maps and appendices.
