Ideally, the sensations of attention should be clear and sharp. For attention on the breath at the nose, the ideal state is something like breathing very cold air on a winter’s day – clear, sharp, intense.

Your attention on the breath will probably never give sensations like that, but the point is that this is the axis to look at : clear and sharp sensations on one end, dull and forgettable on the other. When your attention fades, the sensations will move from the clear end to the dull end.