I stumbled over an article on how important it is in the publishing industry to keep your deadlines. Unless your book is really, really wanted by the publisher, it can happen that they cancel the contract and ask for the advance money back if you don't hand in the manuscript in time. The article claims that this is getting more common although the publishers do not admit to it readily.
Thanks to Holly's course, we do have two big advantages: 1. we learn how to calculate deadlines that we can keep and how to keep them, and 2. we learn to write books that are really, really wanted by the publisher.
Feel free to join us over at How to Think Sideways (if you're not already a member).