When your breathing is easy and deep, your body works efficiently, and your mind settles. That doesn't mean that your balance (in tree pose or anywhere else) will be perfect and your life will be seamless, but you'll be better equipped to deal with the wobbles and earthquakes that get thrown into the mix.
Yoga Cures: Simple Routines to Conquer More Than 50 Common Ailments and Live Pain-Free (ed. Harmony, 2012) - ISBN: 9780307954862