Check this out:

https://halo.bungie.net/images/site/h...chiefanim2.jpg

How come all the surfaces are further subdivided into little triangles? Like the knee pad, it looks like it could just be made out of quadrilaterals, but all the quads got diagonals splitting them into two triangles anyways.

I was thinking maybe it has something to do with the whole "three points define a plane" thing but I'm not sure.