Warning to Facebook app developers: mind reading skills required!

When you submit your app to Facebook's Product Directory, it may be rejected with a very vague reason such as this:

"Thanks for your submission of "<appname>" to the Facebook Platform's Product Directory. We have reviewed your application, and unfortunately cannot yet add it to the directory because it is unfinished or under construction. Please fix this problem and resubmit the application."

Now you get to have lots of fun trying to guess what this is all about. In fact, looking through the Developers' group might give you some ideas. Maybe one day you might stumble upon the reason for the rejection. Or maybe not.