The most common and most likely answer to this crossword clue is the 11 letter word INSOUCIANCE
I've seen this crossword clue in The Times
I
N
S
O
U
C
I
A
N
C
E
Buddy explains!

The straight part
We know that "Carefree attitude" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case carefree attitude = insouciance.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does INSOUCIANCE mean?
INSOUCIANCE noun- Carelessness, heedlessness, indifference, or casual unconcern
- Nonchalance