have an axe to grind

Từ điển Oxford Advanced Learner 8th

ˌhave an ˈaxe to grind idiom
to have private reasons for being involved in sth or for arguing for a particular cause
•She had no axe to grind and was only acting out of concern for their safety.
•These criticisms are commonly voiced by those who have some political axe to grind.
Main entry: ↑axe_idiom