Imagine you’re working on a complex ASP.NET Core application with multiple services: email notifications, payment processing, logging, and data access. At first, you might instantiate these services directly inside your classes. But soon, your code starts to look like a tangled mess of dependencies. Changing one service ripples through the entire codebase, making testing a nightmare and refactoring risky. This is where Dependency Injection (DI) comes to the rescue.