GTD has worked beautifully for completing next actions with defined edges i.e. call so-and-so, buy toilet paper, email so-and-so, etc. Where I struggle with GTD is when the next action (or could be a project) is creative in nature or requires 'deep thinking' such as writing a paper, or creating a design, or strategizing a plan. Usually with these creative assignments, the next action isn't readily apparent or easily defined. What's the best practice for GTD in these cases? I find internal resistance to working on these assignments because it's not clear to me where to start and where it ends, so they tend to get pushed back in favor of the more traditional 'widgets' that can be cranked easily.