Not if the idea sits in someone's head. The execution is extremely important. I've had ideas that pre-dated devices like the ipad and iphone by 15 years, but because I didn't do anything with those ideas, they were essentially useless.
Now the question is, where is the limit beetween an idea and his execution. If the idea is a vague thing like "a computer that fits in my pocket", then it's just a dream. The most details you have about your idea, the most you're move close its execution.
Humans build cities; or robots that build cities, or robots that build robots that build cities.
Or people that build robots that build city-building robots.