When you ask someone if they would use your new product, buy your new widget or participate in your new service once it's ready, you will get a lie in response.
It might be a generous lie ("sure, I love this") or it might be a fearful lie ("here are the six reasons I would never use this"). The fearful lies cause us to scale back, to shave off, to go for mediocre. And the generous lies push us to launch stuff that's just not very good.
People don't mean to mess you up, but you've made the error of asking them to imagine a future they have trouble imagining. It's incredibly different than asking them to justify what they already do. "Why did you buy that particular car?" queries a completely different part of the brain than, "would you buy this new kind of car?"
Imagine the early focus groups for an early modern car. "Why does the transmission say 'd' instead of 'f'? F means forward!" "Why doesn't the window work the way the windows in my house work?" "There should be a lot of warnings on this thing, it could kill someone." "There's a radio? Why don't you make the car good at just one thing…"
It's one thing for someone to explain why they read and liked a particular book. It's another to ask them if they would read it, or even publish it. Almost everyone is horribly bad at this sort of explanation.
Steve Krug has written a really useful book about this. The takeaway is to never again run an amateur focus group, never ask an investor to help you think about what the market wants. Instead, we have to show, not tell, must create environments where people choose, then ask them why.