Interfaces are essential in object-oriented programming, in functional programming (
traits) and, especially, in design patterns. Go's source code is full of interfaces everywhere because they provide the abstraction needed to deliver uncoupled code with the help of functions. As a programmer, you also need this type of abstraction when you write libraries but also when you write code that is going to be maintained in the future with new functionality.
Interfaces are something difficult to grasp at the beginning but very easy once you have understood their behavior and provide very elegant solutions for common problems. We will use them extensively during this book so put special focus on this section.