I made this simple framework to explain why and how we should "depend on abstractions and not on concretions". It's a quadrant diagram where the two dimensions captures the principles "program to interfaces, not implementations" and "dependency injection".
https://geni.us/IBhtLnh (Clean Architecture)
https://geni.us/CpLx2y (Agile Principles, Patterns, and Practices)
https://geni.us/zzlx (Dependency Injection: Principles, Practices, and Patterns)

00:00 Intro
00:14 Overview
00:41 The diagram
02:41 Concretion + Instantiation
05:34 Dependency Injection (Concretion + Injection)
06:36 Program to interfaces (Abstraction + Instantiation)
09:22 Combining both (Abstraction + Injection)
10:01 Book recommendations
10:39 Depend on abstractions (Abstraction + Injection)

Watch next:    • Always Use Interfaces