The most common and most likely answer to this crossword clue is the 10 letter word UNDERVALUE
I've seen this crossword clue in Independent
U
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More clues leading to the result UNDERVALUE
Buddy explains!

The straight part
We know that "Fail to appreciate" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fail to appreciate = undervalue.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 UNDERVALUE mean?
UNDERVALUE noun- An undervaluation; a price or rate below the actual worth.
- To underestimate, or assign too low a value to.
- To have too little regard for.