The point made in the previous section is valid, but it also needs a warning—avoid a dangerous path if it's misunderstood or taken to the extreme.
A base class (abstract or not) defines an interface for all the other classes to extend it. The fact that this should be as small as possible has to be understood in terms of cohesion—it should do one thing. That doesn't mean it must necessarily have one method. In the previous example, it was by coincidence that both methods were doing totally disjoint things, hence it made sense to separate them into different classes.
But it could be the case that more than one method rightfully belongs to the same class. Imagine that you want to provide a mixin class that abstracts ...
