Discussion Topic 1 — The 'diamond of death' class model

It is easy to make a case for disallowing multiple inheritance by considering the so-called `diamond of death' class model. This is a class structure as shown below:

Here D is a subclass of B and C (multiple inheritance), while B and C are both subclasses of A. It might seem at first sight that this structure is unusual, but in practice it can occur quite frequently.

What real-world structures may lead to `diamond of death' class structures?

What are the problems with this structure?