Ask HN: How do you respond when someone says a feature is confusing?

I've seen many arguments where one person will say "That's confusing," without giving a lot of reasoning for why it might be confusing. Often times people who call something confusing understand how the feature works, but believe it would be confusing for others. Is there a way to prove that something is not confusing? Conversely, is there a way to prove that something IS confusing?