Chapter 16 of the Tannishō 歎異抄 is about whether it is necessary to re-"convert" (廻心, literally "turn your spirit around") every time you get angry or mouth off to someone. The answer given is no: "conversion" happens only once, when news of Amitabha's marvelousness first pierces your ignorance and you realize that he's your ticket out of this dump.

The chapter elaborates as follows:

一切の事に、あしたゆふべに廻心して、往生をとげ候ふべくは、ひとのいのちは、出づる息、入るほどをまたずしてをはることなれば、廻心もせず、柔和・忍辱のおもひにも住せざらんさきにいのちつきば、摂取不捨の誓願はむなしくならせおはしますべきにや

This is not a strict translation, but in summary, if it were necessary to re-convert after every single event, morning and evening, in order to be reborn in the Pure Land, we would be in trouble, because "the departing breath does not wait for the arriving one." Every time we breathe out, we don't know if we'll ever breathe in again. We might die at any moment, without having re-converted or reconnected with virtues like gentleness and forbearance. If dying in such a state excludes people from coverage under Amitabha's vow to get everyone into paradise, well, that wouldn't be much of a vow, right? Ergo, that must not be the case, and conversion must not be necessary every time you sneak an extra cookie.

The breath imagery in that passage is a well-known proverb, but I was surprised to find the inhale/exhale pair called into service on the opposite point in a poem by Ryōkan 良寛. ABE Ryūichi and Peter HASKEL's Ryōkan book Great Fool sez:

Someone recited a poem that read:

  The breath going out, the breath coming in
  Over and then over again
  Only leaves me to reflect
  What a fleeting world this is

(izuru iki mata iru iki to bakari nite / yo o hakanaku mo omooyuru kana)

To which the Master replied:

  The breath going out, the breath coming in
  Over and then over again
  Know that this is itself the proof
  That this world never ends

(izuru iki mata iru iki wa yo no naka no / tsuki senu koto no tameshi to zo shire)

Stephen D. CARTER, in his anthology, translates the second poem quite similarly:

The way breath goes out,
and then again breath comes in:
know this as a sign
  that this world we live in
    never comes to an end.

I'm not sure I get what Ryōkan means here. Is it "there's plenty of breath to go around, life goes on; it's not a fragile world, though we who live in it might be"? Or could it be that the translators above are mistakenly adding the "never" and Ryōkan is pointing out that over the course of our lives, every individual inhalation is triumphant proof of our continued existence?