Pulling out your hair because your usually reliable staff just isn't delivering?
Maybe they stopped showing up to work on time
Or the quality of their product just isn't what it used to be
Or they're constantly needing to take time off
What's going on? And what do you do about it?
Usually when someone's work suddenly starts to slip there's something going on. The usual approach is to keep berating the employee and hassling them about whatever it is that they aren't' doing right anymore. This usually isn't effective and there is another way.
Maybe the person is relapsing. Maybe they are having family troubles. Maybe they're just wrapped up in the throes of a new romance. Your job as the employer isn't to figure out what's happening in your employee's personal life.
Your job is to figure out if there is anything going on at work that is contributing to their change in behavior and see if there is anything you can do to fix that. Maybe there is a system that isn't working well, or maybe their co-worker isn't getting them information on time. This is where you do your digging to see what you can do to help.
Once this is fixed (if there is anything) then it is time to name the drop in performance and request a change. Be specific about what you are asking for and when you expect it to happen. Be clear about any consequences that there are if the employee isn't able to change their behavior.
Last, follow up. If the behavior isn't changed then follow through with those consequences. If the behavior is changed, thank the employee and move on.