It isn't a dichotomy, but it is like a person trying to support their weight on the floor. The straighter they stand, the long they can keep the position. Have them lean far enough over and it is near inevitable that they will eventually crash to the ground. If you have them plank a few inches off the ground, you could probably hold your breath longer than it takes for them to hit the ground.

(I think I need a better analogy here, but it'll take me some time to come up with one.)