Stephen Levine in his book, Gradual Awakening, talks about the importance of the balance of awareness, concentration and energy in mindfulness meditation. We can strengthen and cultivate our awareness and concentration by choosing to focus our attention on our breath at a specific point, either the nostrils or the belly. He encourages us to stay at one point and not to move between the two, thinking one is better than the other. He explains that 'Going from one spot to another is like digging several shallow holes for a well. If we want to hit water, we dig deep straight down in one place.