Courage or sheer good fortune, on the quiet (5)
I believe the answer is:
pluck
'courage' is the definition.
(I know that pluck is a type of fearlessness)
'fortune on the quiet' is the wordplay.
'fortune' becomes 'luck' (synonyms).
'on' says to put letters next to each other.
'the quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'luck' after 'p' is 'PLUCK'.
'or sheer good' acts as a link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for pluck that I've seen before include "Play a guitar - prepare a chicken for the pot" , "Remove feathers" , "Nerve" , "Determined courage" , "extract" .)