Be fully aware that you are no stranger to (4,4)

I believe the answer is:

know well

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'aware that you are no stranger to' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.

'be fully' is the wordplay.
'be' becomes 'know' (I can't explain this - if you can you should believe this answer much more).
'fully' becomes 'well' (synonyms).
'know'+'well'='KNOW WELL'

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