Single Responsibility Principle

Single Responsibility Principle - Class should only have one reason to change

When we allow a class to not only take care of its own business (managing some kind of aggregate) but also take on more responsibilities. then we've given the class two reasons to change.

We know we want to avoid change in a class like the plague; as modifying code provides all sorts of opportunities for problems to creep in. Having two ways to change increase the probability that class will change in the future and when it does, its going to affect two aspects

Every responsibility of a class is an area of potential change. More than one responsibility means more than one area of change.
The Principle guides us to assign responsibility to one class and only one class.

Separating responsibility is one of the hardest things to do. The only way to succeed is to be diligent in examining your designs and to watch out for signals that a class is changing in more than one way as your system grows.