Perseverance shown by foolish individual — one I put into service (9)

I believe the answer is:

assiduity

'perseverance' is the definition.
(thesaurus)

'foolish individual one i put into service' is the wordplay.
'foolish individual' becomes 'ass' (ass can mean a foolish person).
'one' becomes 'i' (Roman numeral).
'put into' is an insertion indicator.
'service' becomes 'duty' (I've seen this before).
'i' going into 'duty' is 'duity'.
'ass'+'i'+'duity'='ASSIDUITY'

'shown by' is the link.

(Another definition for assiduity that I've seen is " constant attention".)

I've seen this clue in The Times.

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