It's not stated when one is beset by discretion (5)
I believe the answer is:
tacit
'it's not stated' is the definition.
I can't tell whether this defines the answer.
'one is beset by discretion' is the wordplay.
'one' becomes 'i' (Roman numeral).
'is beset by' is an insertion indicator ('beset' could historically mean 'cover').
'discretion' becomes 'tact' (being tactful is being discreet).
'i' put within 'tact' is 'TACIT'.
'when' is the link.
Can you help me to learn more?
(Other definitions for tacit that I've seen before include "Understood without being directly expressed" , "Unvoiced" , "Not said though understood" , "without speaking" , "Unspoken but understood" .)