I heard a quote not related to programming, but fits it well.
Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away. - Antoine de Saint-ExuperyThis is a great way to explain the single responsibility principle for classes. Classes should have a single purpose and not be a jack of all trades. Kind of like an over sized Swiss Army Knife can do it a lot, but it doesn't do most things better than a purpose built item.
In programming, classes that have a clear and specific purpose makes them more testable and reusable.