If you say you’ve just been to the doctor, my default stance will be to believe you. But if you say you’ve been in an extraterrestrial vehicle where little gray beings ran medical tests on you, I’ll need more than your word. The claim you’re making (aliens!) is so far outside the bounds of what our everyday experience offers, that I’ll need additional proof. Grainy photographs won’t be enough.
Carl Sagan used to say that extraordinary claims require extraordinary evidence. This skeptical stance is healthy. You’re not saying “I’ll never believe this!”; you’re saying “I’m open to hearing you out — but this’d better be good!” Good decision-making calls for clarity; seeing things as they really are. This may be different from how we’re told they are. And not just by others: we can easily fool ourselves, crafting fantastic stories about the way things are.
As designers, we’re charged with conceiving different ways of doing things; different ways of being in the world. Our sketches and prototypes create simulations of what things would be like under different circumstances. The better we are at this, the more we are at risk of believing our alternate realities. This is one of the reasons why testing is so important: it helps provide validation for our hypothesis. The more outlandish they are, the more validation is needed. (The ultimate validation: a product or service that succeeds in the market.)