[staunch]

Procrastination is often your gut telling you something is wrong. It very well may be that his unconscious mind knows it's not worth the effort to complete the project.

Move on to product 2. If it happens again, maybe it's a different problem, but it could easily be that he's right about product 1.

This is the most important reason why you need to work on things that you deeply believe in. Unfortunately you only find out late in the game how much you really care about a problem.

[dholowiski]

I agree- he has a deep understanding of the product and even if he can't express it, he probably understands on some level why it _just wont work_. He could be having personal issues or, and this may sound crazy but depending on how far north of the equator you live he just might not be getting enough sunshine (seasonal affective disorder).