Idippaarai illaadha emaraa mannan keduppaar ilaanum kedum. A king without people who rebuke him will be ruined, even with no enemies to ruin him. This is couplet 448 of the Thirukkural, the classical Tamil book of ethics.
In his note on the couplet before it, the commentator Parimelazhagar describes such counselors as people who come close and speak up when they see wrongdoing.