Put another way: the only thing that you can verify when communicating that the sky is on fire is that the other party knows you think the sky is on fire. Whether or not they think the sky is on fire, or whether they think you're blowing hot air, is pretty inscrutable. If they don't agree with you, they're still likely to not show it because you (to them) are a neurotic hothead who they don't want to upset.
The only truth in what you manage to communicate to people is the effect it has on how they act. In other words - they can't tell you anything! They can only show you.