How do I tell someone on my team their work isn’t good enough?

I manage someone and need to talk to them about . Two specific things that happened: . What I want to be different a month from now: . I’ve left out their name and anything private about them. Ask me up to three questions, one at a time, about whether I’ve raised this before and what may have changed for them lately. Then plan a 20-minute conversation: a two-sentence opening that states the problem with no compliment sandwich, each example as what happened and what it caused, two questions that let them give their side, and a next step with a date. End with what I might have wrong about them, the part I may have played, and the sentence I’ll be tempted to say and shouldn’t.