Prodigy's flaw ultimately: not good enough! (10)
I believe the answer is:
wunderkind
'prodigy's' is the definition.
(I've seen this before)
'flaw ultimately not good enough' is the wordplay.
I cannot quite understand how this works, but
'not' could be 'un' (prefix meaning 'not') and 'un' is located in the answer.
'good' could be 'kind' (associated in meaning) and 'kind' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for wunderkind that I've seen before include "One having early success" , "Child prodigy" , "Extraordinary issue" , "Perhaps Mozart" , "Clever young person" .)