Prototypes give you something to talk about and to point to.
“Collaboration in UX is more important than in other fields. Why? UX is all about communication. The dangers of insular thinking in UX are that other people can’t relate to our ideas, even if they are good. When people say “an engineer designed this,” it’s not because engineers are stupid or haven’t thought the problem through. It’s because their values (consistency, supportability, development costs) are not the same as the values of the user (easy, intuitive, powerful).”