Yoga teaches us that the breath, mind, and nervous system are intricately linked. If the breath is shallow and rapid, the mind is erratic and the nervous system destabilized, indicating a state of stress or the fight-flight-freeze response. Take a deeper, fuller breath and you immediately feel calmer and clearer.
In other words, the mind mimics the breath: shallow, rapid breathing creates quick, rapid thoughts; slow the breath down and thoughts slow down; breathe in a one-to-one ratio inhale-to-exhale and the mind steadies.
Focusing on the space between the breath helps create a gap between our thoughts, calms the mind, and is an easy to learn meditation for becoming more present in a pinch.