Impermanent.

There are only two states of human mind:

Happiness and suffering.

They are compounded things of the mind, compounded mind formations.

A breath is a compounded material thing.

All compounded things are impermanent;

prone to rise and fall;

having risen, they're passed away,

their passing truest bliss.

A breath is born and passed away naturally and normally;

no effort requirement, no stain in the mind; tranquility and mindfulness.

In meditation, people just do one work:

know their normal breath in and out naturally.

That is a breath passing its truest bliss.

 

The meditation people can have a mindfulness while the breath is in and out.

Happiness and suffering should be born and passed away with a mindfulness also.