Finding fault is vital (8)
I believe the answer is:
critical
'finding fault' is the definition.
(I've seen this before)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for critical that I've seen before include "Extremely ill, near death" , "Finding faults" , "expressing disapproving comments" , "giving literary analysis" , "essential" .)