Because flesh is weak? (7)

I believe the answer is:

selfish

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'weak?' is the definition.
Both the definition and answer are adjectives. Perhaps they are linked in a way I don't understand?

'because flesh is' is the wordplay.
'flesh is' can be anagrammed to 'SELFISH'.
However, I am not clear how the anagram is indicated.

Can you help me to learn more?

(Other definitions for selfish that I've seen before include "Concerned only with one's personal welfare" , "Concerned only with oneself" , "Concerned chiefly with one's own interests" , "Ungenerous" , "Concerned only with self" .)

I've seen this clue in the Evening Standard.

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