"Think nothing for 5 minutes" is not like "raise my right arm." It is like "hold my arm so still for 5 minutes than a careful observer will not even notice a jitter." It is unlikely that anyone can do either of those things on demand. But I can refrain from most complete thoughts for 5 minutes, and from large motions of my arm. My control over my thoughts is actually very similar to my control over my arm. You find dissimilarity because you are comparing the wrong things.