Sometimes, we think like:
genius idea, I do not need any validation. I'll just make it and everyone will like it
99% of cases it passes through unmentioned. Not because it is bad. Mostly because you did not make enough effort to promote it to your audience.
Note that you can't properly validate ideas with the audience; you have to validate a solution around your idea. It's super hard to get the set of features and UX right even when you have the 'right' value proposition.
I believe we could mitigate both problems with more dedicated forums to discuss ideas in a structured way (a kind of flea market for ideas).
That was my intention when I started a while ago: https://github.com/marcelosousa/million-dollar-ideas.
I think marketing is the biggest factor. For example, I built an app that uses a reverse BAC formula to calculate the amount of alcohol for a party. I thought I should market it to college students (just put up posters on a campus). I didn't have much success, probably because of the bland UI or that college kids are more laid back about planning.
Someone suggested I market it to event planners or caterers for doing weddings, etc. I think this would be more successful since they need a calculator more than a cool UI. I don't want to pay for promoting it though.
Nobody actually know what they really want before they see it.