People who have played Diplomacy a bit have a kind of sense of which plans are workable and which are unworkable. For example, it's known that while playing Germany, an attack on England or France is workable whereas an immediate attack on Russia or Austria is tantamount to suicide. Yet Turkey can attack Russia, Austria, or Italy and all of these plans are workable. The question is: What makes a plan workable or unworkable?
Some people think that Diplomacy is about getting centers -- and they're right, to a certain extent. However, some centers are more valuable than others. Generally speaking, centers along the sides and edges are more valuable than those in the center. Why? It's because these centers usually don't need to be defended. Think of a successful England, for example. He will have London, Liverpool, and Edinburgh -- three centers that do not require defense. This will allow him to use three units to go out and conquer more.
Poor Austria, on the other hand, can usually get up to 5 centers without too much fuss. However, he will often find it necessary to occupy every center in order to defend it. He will have no spare units with which to conquer more.
While it's not possible to enumerate every workable plan, here is an example of a workable (KoD) plan for a solo victory:
Playing France, start by locking up the southwest corner of the board. This will give you Spain and Portugal as centers that don't need defending while you go off in search or greener pastures. Then, team up with Germany to invade England. That will get you into another corner. Next, help Germany against Russia while invading Italy to get Tunis. Once you are over the stalemate line, stab Germany FTW.
Why is this plan workable? Because you will get multiple centers that don't need defending. If you are successful, soon you will have Spain, Portugal, Paris, Brest, Marseilles, London, and Liverpool -- none of which will need defending.
Could this plan go wrong? Of course it could! You might end up with England and Germany allied against you. You might succeed in killing England only to find that you are facing a Central Triple Alliance that puts Italy and Germany at your throats. You may fail to get over the stalemate line when time comes to take on Italy. You may stab Germany but fail to get the win. None of these problems, however, makes the plan unworkable.
What plans do you consider workable or unworkable? Why? I'd like to know.