Jason Cohen in the Smart Bear Live! podcast, on talking to thirty people before you start building a prototype, to find out who would buy it and what they'd want you to build (starting at 1:33:58):

"It sounds so easy – "I'll just go talk to them and discover some stuff." It's really hard and most people don't do it. Like I'm telling you this, and if I had to bet, I would bet – definitely, like, very good odds – that you won't talk to anyone. And the next best odds is you'll talk to maybe three people and then make a decision one way or another. Neither of those is right. But that's what most people do. […] You tell them to go talk to thirty people. They hear me say "thirty people" and they're like "eh" and they'll talk to three people and they sort of make up their mind. That's not it! It's thirty people! Not three, thirty!"