It curtails tendency to be unselfish (10)

I believe the answer is:

altruistic

I'm a little stuck... Click here to teach me more about this clue!

'unselfish' is the definition.
(associated in meaning)

'it curtails tendency to' is the wordplay.
'it curtails' can be anagrammed to 'ALTRUISTIC'.
Though, I am not clear how the anagram is indicated.

'be' is the link.

Can you help me to learn more?

(Other definitions for altruistic that I've seen before include "magnanimous" , "in others' interest" , "Selfless" , "Humanitarian" , "Concerned for others' wellbeing" .)

I've seen this clue in the Sydney Morning Herald.

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