Triangles are just a convenient way to frame the three-dimensional relationship. Theoretically you can take it to any number of dimensions with fairly obvious extensions to the definition; however, it starts to become computationally expensive and human-impractical to gain much understanding that way.

This is why almost no matter what you put on the points of the triangle, it works; as long as on the frontier there is at least some opposition, it works. The times you can have all of X and all of Y are rare, and all of three things essentially unheard of.