Yale law professor Ian Ayres walks through Jacobs & Youngs v. Kent, the classic contracts case about a builder who installed the wrong brand of pipe. Drawn from his American Contract Law course, the lecture uses the case to introduce the doctrine of substantial performance and the courts' reluctance to force literal compliance with contract specifications when a breach causes no real harm. Ayres explains Judge Cardozo's reasoning distinguishing willful breaches from trivial deviations, and how damages get measured when specific performance would be wasteful, comparing cost of completion against diminution in value. The talk sets up the case as an entry point into broader questions about contract interpretation and remedies that recur throughout the course. It runs a tight fifteen minutes, aimed at students beginning to work through foundational contracts doctrine.