I've noticed this a lot - I think people are far too quick to take face-to-face positive feedback at, no pun intended, face value.
To me, it seems like a pretty elementary mistake, but I think that oftentimes people are more subconsciously desiring external validation than accurate assessments.
can't remember where I heard this but the advice was basically this: When pitching your idea, and generating excitement, ask for money (or a commitment) on the spot. There's a big difference between saying you'd pay for something, and paying for something.
The flip side is that sometimes it takes awhile to build the perception of value, hence free trials/freemium models. Get people hooked, then ask for $.
There are many ways to be successful (and even more ways to be unsuccessful).
This chimes a lot with what I've seen, and indeed, what I do myself. I had a few friends plough hard-earned money into a really bad start-up idea (basically an inferior pay-walled Wikipedia), and instead of telling them what I really thought of it, I weaselled out saying something bland, non-committal and mildly supportive.
To me, it seems like a pretty elementary mistake, but I think that oftentimes people are more subconsciously desiring external validation than accurate assessments.