When we practise awareness of breathing, we think that we should not have thoughts, that we should not have other sensations, that we should not hear sounds, so we try to exclude them and only be with the breath, and that can create lots of tension and lots of suffering. I would suggest instead that we do it in this way: just knowing, just having awareness of what is happening and then allowing calm to come naturally. You can never get it by force, you can never get it by trying. This is maybe why in the text it is said that when there is loving-kindness the mind becomes calm naturally. So rather than hating things, rather than fighting things, resisting things, controlling things, you just know what is happening, then let calm arise naturally.