>I agree with you on MustOverride.
>It's like creating an interface or an abstract class in Java, the derived class must override the method.
>
>I'd like to stree that the inheritance contributes the power of the object oriented programming.
>Therefore, all the method must be overridable. We do not have to say it. If we cannot override method freely, what's the purpose of using the OO language.
>That's why, the keyword overridable and overrides are redundant to me and the fact that we cannot override methods without them defeats the purpose of the OO programming in my mind.

I could be wrong, but I think by default all classes are overridable without specifying the keyword.