Ahhhh, I think I’m getting it.  The link between breath and negative emotions, that is.  Its like this…

Negative emotions tense you up — Being tense effects your breathing — Uneven breathing creates stress in your body — Stress gives you negative emotions

AND AROUND YOU GO

Its a downward circle of stress and we just don’t realise that we’re doing it to ourselves. Knowing all of this doesn’t stop it from happening but it does mean that when you catch yourself spiralling downwards you have a shot, a chance of stopping the rollercoaster descent into frustration.