Yesterday I talked about all the awesome things an idea can have. As a writer and a GM I can't begin to tell you how amazing an idea can be. The beginning of a world, the beginning of a story. Ideas hold nothing but promise. However, you need to be careful - especially if you want to build a game or story - when dealing with ideas. They're dangerous things. Here's why.
The first thing to test an idea against is how shallow it is. The problem with a shallow idea is that it seems like a really good idea with depth and lots of applications until you begin to dig into it. Suddenly you find that the idea doesn't have the depth, doesn't stand up to any real tests, and just kind of leaves you there with nothing to do. An example of this would be a game where the idea is to have the PCs fight against an evil overlord, only the idea doesn't supply the hows, whys, or whats that could be involved in this. Something that doesn't catch you until it is too late.
The second thing to test an idea for is how narrow it is. This is kind of like shallow but in another direction. Instead of lacking depth this one lacks width. An example would be the inception for a lot of mecha games where everyone gets so wrapped up in the idea of the people piloting the giant robots that they forget about all the other people in the game who may want to do something else. This ends up with a game where players may feel shoe horned into being a specific thing, or alternatively the character sheets all come out looking very similar to each other.
Lack of Planning
In both of these cases the core problem is the lack of planning. The person with the idea gets so wrapped up in the idea itself that they forget to explore it, to test it, and to make sure that there is something in there beyond one specific scene or idea. Sure, it is awesome to have the idea of a transforming jet/human mode mech that fights giant aliens, but if you don't think about the things around that you find yourself hitting a wall. Worse, in a game your players may feel like they're hitting a wall. That is going to lead to a lot of frustration and fast.
One way to fight both problems is to not go into a world/game with only one idea. Instead, bring a couple with you. You take your game about giant robots fighting giant invading aliens, combine it with your idea for magical girls transported to another world where they battle an evil sorcerer and not only do you get more stuff to work with you help fix both the problem of shallowness and width at the same time.
Think It Through
The other thing, obviously, is to think your ideas through. Write down the idea, walk away, and then come back to it. Think what the first questions would be in your head if someone told you this and try to answer them. Think how those answers would apply to other things that may be going on and plan it out. Work them together think them through and who knows, you just might end up with one hell of a crazy idea on your hand.