Definition of "project"
A big "a ha" that I had about defining projects came several months ago, when I realized how much "vagueness" was filling my project list. I took something from David Allen, probably from GTD, but I can't remember exaclty where from, the idea to define the successful outcome of a project in terms of something that you can achieve a "win" from, regardless of what other people or circumstances decide to do for or against you.
The classic example is in defining the successful outcome of a particular sales presentation along the lines of:
project : Sales presentation to client X
successful outcome: I have maximized Client X's opportunity to buy from me [instead of "Client X has bought from me"]
I also realized the importance of distinguishing projects from longer-term goals, and by definition, since then, I always ensure (in weekly review as a failsafe point) that all projects on my list are defined in terms of a "short-term end point".
One of the fundamental keys to 'doing' GTD is in the processing phase, which is where we turn "stuff" into "widgets". Generally, I aim to complete all processing in a sitting, but there is certain types of 'stuff' that arises which is vague, and which needs a project in order to complete the processing fully, such as the "look into y" or "Figure Out What's Bothering Me about X", which started this thread. Either way, there's no way around the hard thinking that needs to be done sooner or later to keep the "stuff" from occupying your head.
So, along these lines, "Decide how to define X as a project" can be a valid item on the project list, or its short-form "Look into X". As long as it is on your project list, you will review it regularly to decide on possible next actions.
The caution is not to use this as a way to avoid the minute or two of hard thinking that can be done during processing, and likewise not to leave this on the project list out of the usual vagueness-procrastination patterns that have been discussed in many other contexts here.