This lecture clearly teaches that our work isn't just simple design and code writing, but understanding real-world customer problems and solving them through software. To someone who has only learned server, API, and databases, it's not easy to understand what it means to "develop in a customer-oriented way." Someone might tell them that using "Clean Architecture" or "Ports and Adapters" architecture makes it easy to handle changing requirements. Even after studying hard and applying patterns, it's not easy to feel like you are developing in a customer-oriented way. This lecture provides clear guidelines to such people. The content taught in the lecture is about well-organizing customer requirements and writing code that fulfills them. And in this process, it lets you realize how effective "Test-Driven Development" is. If you follow the lecture to the end and pay attention to its purpose, the question mark you have about TDD will turn into an exclamation mark.