As long as you control the product entirely, I believe that it's possible to break tasks down into one-week chunks. But what happens when you depend on external

As long as you control the product entirely, I believe that it's possible to break tasks down into one-week chunks. But what happens when you depend on external parties to complete your task? If they don't delivery, or if it just takes a lot of pm legwork to get things moving, a technically simple task may well take many weeks to get through.