Recognise one with all-consuming interests being upset (4)

I believe the answer is:

know

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'recognise' is the definition.
(know can mean to recognise someone)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for know that I've seen before include "Recognize" , "Be acquainted with" , "Be sure of something" , "Be aware of (something)" , "Understand" .)

I've seen this clue in The Guardian.

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