>Don’t launch a product until you’ve put a prototype in front of a few customers and gotten feedback. Make sure that they say that they’ll find value in it – key questions include things like “how would you use this feature?”

I (and several others) found that it doesn't always work. There's a gap between "I'd hypothetically use it" and "I will actually use it". It's often the case that, when asked if they'd use a certain feature, potential customers often say "yes" but when the time comes around to actually using the feature/product, no one suddenly cares. I've seen several articles describing this interesting phenomenon, but I can't find the links.