Advice to have effect mostly on individual? Mostly (7)
I believe the answer is:
counsel
'advice' is the definition.
(I've seen this before)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for counsel that I've seen before include "kept by the secretive" , "Guidance" , "Legal advice" , "Lawyer who pleads cases in court" , "Legal adviser" .)