The strongest lock means nothing when the enemy already has permission to live inside.

Protection against outside threats does nothing about what you have already let in. The habit, the relationship, the pattern of thinking that has full access is not affected by any of your defenses, because it was invited and it is already inside.

Ask what has unrestricted access to your time and mood. If something in that group consistently harms you, the work is there rather than at the perimeter. Internal access is the harder thing to revoke and usually the more important.