It's not a case of not understanding, it's a case of not believing. If you're talking to a lay person that trusts you, they may raise such an objection, but the

It's not a case of not understanding, it's a case of not believing. If you're talking to a lay person that trusts you, they may raise such an objection, but they'll believe you once you reply "that can be, and often is, faked". Belief is a thorny issue when trying to communicate to the masses, though.