- It's uncomfortable. You are typically so excited about an idea that the thought of learning it doesn't have mass appeal is uncomfortable. People avoid uncomfortable realities. In other words: "I KNOW this is a great idea, I just KNOW it. If I don't build this NOW, someone else will beat me to it. I don't have time to waste talking to customers. If Henry Ford would've asked people what they wanted, they would've said a faster horse."
- People are proud, if they're going to show a product to their friends/family, they want to make sure it's well-built, fully featured, etc... The idea of "just getting something in front of customers that works" aka an MVP is embarrassing for some people. They think that if they release a "amateur" product, people will think they're amateur.
- People are irrational. They think that their idea is so special that asking people about it, getting validation, etc... could make them a target for idea theft. So they isolate themselves, validate with a few close friends (who are unlikely to give honest, brutal feedback) and build a huge product so that when they launch, they'll be far ahead of their competitors. The problem with this is that you'll likely build the wrong product the first time around.
I'll add that, for the tech minded, building is easy in comparison to validating. Just fire up the IDE, write code, and debug. Validating involves putting your idea (and by association, yourself) out there for the world to potentially ridicule... and then trying to convince people to open up their wallets to your idea. Not so easy.
also it is a chicken-egg dilemma. It's hard to validate without a prototype. (I know the dropbox story, it won't work in all cases.) sometimes, a product is trying to improve user experience, not about an innovative idea. I think that user experience has to be felt.
I also feel that customer interviews might be misleading sometimes. I remember when iphone was launched first time, it was way pricier than other cell phones. A lot of people were nay sayers including myself.
If you put up a landing page and people immediately start buying, great. What happens if you get no conversions? Is it the product, market, your marketing? How much effort/money do you put in before you say it's a negative result?
marketing is an adverse learning environment, and beginners typically misattribute the cause of failure. It's difficult to learn incrementally via trial and error, unlike coding.
the best way to mitigate "no market need" is to solve an existing pain (that the market is already buying) rather than inventing new ones.
Agreed that it's easy to think you've validated by getting a handful of people to nod enthusiastically at a Powerpoint!