The most common and most likely answer to this crossword clue is the 12 letter word SELFLESSNESS
I've seen this crossword clue in The Daily Telegraph
S
E
L
F
L
E
S
S
N
E
S
S
Buddy explains!
The straight part
We know that "It’s not in one’s own interest to display it" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case it’s not in one’s own interest to display it = selflessness.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 SELFLESSNESS mean?
SELFLESSNESS noun- The quality or state of being selfless.