When a building leaks, settles, or costs twice what it should, the question of whether the designer is liable turns on doctrines that surprise almost everyone involved. This article explains why a design professional is not liable for producing a perfect building but only for exercising the care of a reasonably prudent practitioner, and why that distinction defeats more claims than any other. It covers the implied warranty a designer's plans carry to the contractor, the economic loss rule that blocks tort claims for pure financial harm and the exceptions that swallow parts of it, and the certificate-of-merit statutes that require an expert affidavit before a complaint can even be filed. It explains the betterment defense that reduces damages to the cost of the error rather than the cost of the correct building, the statutes of limitation and repose that end claims on a schedule, and the insurance architecture that determines whether any judgment gets paid. It closes with contract administration duties, site safety, and what actually goes wrong on projects.