Why is Interfaces important in Laravel applications, and what problem does it solve for developers?

Why is Interfaces important in Laravel applications, and what problem does it solve for developers? The key reason to understand interfaces is that Laravel applications are usually composed of several layers that must work together predictably. Interfaces let application code depend on a contract while the container chooses a concrete implementation. Ignoring that boundary can lead to duplicated logic, poor security, unnecessary database work, or code that is difficult to test. Why it matters in practice: Laravel's service container resolves class dependencies and supports dependency injection, enabling services to depend on abstractions or collaborators without constructing them manually. The specific focus here is interfaces: Interfaces let application code depend on a contract while the container chooses a concrete implementation. This question is designed to test not only terminology, but also how the concept fits into Laravel's request, application, database, security, or deployment workflow.