Dictionary:

insouciance

  (ĭn-sū'sē-əns, ăN'sū-syäNs')

Blithe lack of concern; nonchalance.

What, me worry? I'd much rather be insouciant and untroubled, like South Korea seems to be in the face of test missiles launched by its northern neighbor and former enemy:

"To a great extent, though, the South's insouciance about the North's threat is the product of years of peaceful relations."

Link: Launchings put Japan and South Korea on different paths

Posted July 13, 2006.

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The noun has one meaning:

Meaning #1: the cheerful feeling you have when nothing is troubling you
  Synonyms: carefreeness, lightheartedness, lightsomeness