Something has gone wrong, and it has reached a patient. The wrong dose was given, the result sat unread, the wrong site was marked. You are the resident in the room, often the first one to it, and two instincts pull at you. One says apologize for everything, right now. The other says say nothing and wait for the attending. On its own, each one can hurt you and the patient.
Start with what the law actually rewards. Most states have an "apology law" that keeps an expression of sympathy out of a later malpractice case. But in most of them the shield covers sympathy only, not an admission of fault. "I'm so sorry this happened to you" is protected. "I'm sorry, I made a mistake" often is not. The line varies by state, and you will not be looking it up at the bedside. That is why the habit has to exist before you need it: lead with empathy, never with blame.
The deeper reason is not legal, it is human. Patients sue far more often because they felt abandoned or lied to than because an error occurred. The hospitals that moved from "deny and defend" to early, honest disclosure (Michigan's program is the most studied) saw claims and legal costs fall, not rise. Silence reads as a cover-up. Honesty, handled well, protects you.
So here is what works. Tell the patient you are sorry this happened. Say only what you know, plainly: "Here's what we know now, and what we don't yet." Don't guess at the cause. Promise a next step: "I'll find out exactly what went wrong and come back to you." Then keep that promise.
Here is what backfires. Speculating before anyone knows ("I think the night team missed it"). Naming fault, yours or a colleague's, before any review is done. Early theories are usually wrong, and those are the ones that follow you. The other danger is panic: going quiet because you are afraid, or worse, altering, back-dating, or deleting a note to cover yourself. Changing the record turns a defensible error into an indefensible one.
One rule sits above the rest: as a resident, you do not run this conversation alone. The moment you learn an error reached a patient, tell your attending and call risk management. Formal disclosure is the institution's responsibility, and most hospitals have people whose job is to handle it with you. Your part is to be honest, stay present, and bring the right people in fast.
Say the true thing. Not the unproven one.