The mind does not stay all the time with the feeling of breath. It goes to sounds, memories, emotions, perceptions, consciousness, and mental formations as well. When we experience these states, we should forget about the feeling of breath and immediately focus our attention on these states -- one at a time, not all of them at one time. As they fade away, we let our mind return to the breath, which is the home base the mind can return to from quick or long journeys