Often, candidates have a hard time expressing their abilities in an interview. Rightfully so: there is plenty that can go wrong like nerves, preparation, and miscommunication. The worst that can happen is if you reject a great candidate candidate because they haven't given you "the right answer™"
We're running an experiment for hires in our product team where we actually want everyone to get a fair, decent shot at it: we want to make interviews about their competence - not anything else.
That way we can make the process about the things that matter: the candidate's potential, and nothing else.