In Catan, there are five resources: wood, brick, wheat, sheep, and ore. You get two free settlements that can access up to three resource hexes for a total of six. An "ideal" placement will let you access two hexes of one resource, and one of each of the other four (that is, all five). But sometimes, this is not practicable, and you have to choose four resources to access with your first two settlements, "neglecting" the fifth. In that case, how do you choose which resource to do this with?
I would imagine that you might "neglect" a resource that you can trade easily for, or be able to access quickly with a third settlement. And that you would come to these conclusions after studying the board. How would these considerations, or others I haven't mentioned, impact your decision?