I think there's a long, long list...
-Falling in love with the idea, the technology, the concept rather than the result/benefit to the buyer.
-Working in the business instead of on it.
-Rigid, inflexible thinking. Not willing to change and adapt (you saw this when the internet first came along). Resistance to change.
-Not differentiated from the start. No compelling reason to buy from them vs their competitors.
-Trying to do too much; trying to do everything and appeal to everyone.
-Believing too much glamour and too much hype. It's not all romance.
-The product just isn't practical (like the Segway scooter). Just too expensive for most people.