I like the answer "right now". We have to assume that we're already, at this moment, wrong about something important. We always find out in the future that our past selves were wrong; hence, we are presently wrong. It's science's mission to figure out what we're wrong about. It's also dangerous to get angry at people who question science, as if we can't question science, we can't really do science. When someone asks for proof or says something isn't real or true, it's science's job to provide the proof.