Answer: Ah, this is the magic of GTDNext. GTDNext is based on the Getting Things Done methodology and uses the next action list concept to display only the current next action for all of your projects.
The genius behind this approach is that you are able to see a concise list of all of your next actions, the items you can do right now, without having to see all the other action items for your projects. This helps prevent you from being overwhelmed by see potentially hundreds of actions that you are unable to do right now, every time you switch to your action list.
Overwhelm one of the biggest problems in other task management applications. Imagine having 20 projects, each project with an average of 5 actions. In most task management apps the user would be presented with 100 actions every time they look at their list. In GTDNext, you will only see 20 actions. A much more manageable view.
Of course you can override this functionality if you have several items in a project you want to appear on your next action list. Just click the "Force Next" box to force the item to show on the next action list. Or you can click the grey "N" in the main view to turn in Green. Notice the very small "F" that is attached to the green square now. That's how you know the item was "forced" to the Next action list.
You can also "Force Next" an entire project in the same manner. When Force Next is applied to a project than any new items added to the project will automatically have Force Next applied.
This video on the Force Next function will help explain how this works in more detail. (best viewed full screen)