How do I finally talk to an employee who is underperforming?

You have carried this for weeks, maybe months, and the weight has not eased — it has grown. Every day you delay, the gap between what you expect and what you say gets wider. The person keeps working, unaware, while you quietly build a case in your head they have never heard. That is not fair to either of you. The kindest thing you can do is tell them plainly, early, while there is still room to fix it. Feedback withheld is not mercy. It is a door closing slowly on someone who does not know it is moving. Most people would rather hear the hard thing and get a chance than be surprised by it later. Book the conversation for this week. Prepare one clear example of the problem and one clear picture of what good looks like. Keep it direct and warm. You are not attacking them. You are giving them the truth they need to improve.