You don’t have to defend every boundary out loud. You just have to keep it.

Limits announced and then crossed teach people that your limits are a conversation. One kept quietly, with no speech attached, teaches them something far more durable. You do not owe anybody a justification for what you will not do, and arguing about it tends to invite negotiation. Behaviour is the only version of a limit that people believe.

Take the one you keep explaining and stop explaining it this week. Just do the thing: leave at ten, phone off after midnight, no to the extra shift. If somebody asks why, the short honest answer is that this is what works for you.