As nouns the difference between blitheness and insouciance
is that blitheness is the characteristic of being blithe while insouciance is carelessness, heedlessness, indifference, or casual unconcern.
blitheness
English
Noun
(-)
The characteristic of being blithe.
insouciance
English
Noun
(-)
carelessness, heedlessness, indifference, or casual unconcern
nonchalance
Synonyms
* See also