My response to that question is to say that it is not about "enough" but about variety and extra happiness.
I try to relate it to parents who want another child. Was the first one not good enough? People don't see it that way. They see it as additional love and fun added to the family. You can say that it is analogous to a poly relationship.
If the child example does not work, you can try the idea of owning more than one pet. Or you can try to relate it to food where you have a favorite, but may want variety.