I think I read it through HackerNews, pretty sure that Drive points out that time constraints are not a motivator.

Here's a google. http://www.emeraldinsight.com/books.htm?chapterid=17055118

Essentially, time constraints hurt autonomy and therefore creativity. If you have a deadline, you are more likely to find the quickest way that works as opposed to the best error free, scalable long term strategy.