I read that too some time ago. I understood that once you announce your project, you get some of the social credit for it. This "advance credit" diminishes the return on actually putting down the work, which also tends to become more tedious towards the end of the project.

I observed this with myself: many years ago I was planning to write a novel. I had already sketched out the plot etc., and of course told my friends a family about it. For about half a year, they kept asking me about the progress. In retrospect, I quite enjoyed being "an author" in their eyes. It seems I did benefit from announcing my project without actually ever finishing it, which may very well have lowered my motivation to pull through with it. Anecdotically QED, I guess...