What he said.
"One of the things that really hurt Apple was after I left, John Sculley got a very serious disease, and that disease, I have other people get, too. It's the disease of thinking that a really great idea is 90% of the work, and that if you just tell all these other people, "Here is the great idea," then, of course, they can go off and make it happen. And the problem with that is that there is just a tremendous amount of craftsmanship in between a great idea and a great product. And as you evolve that great idea, it changes and grows. It never comes out like it starts because you learn a lot more as you get into the subtleties of it and you also find there is tremendous tradeoffs that you have to make. There are just certain things you can't make electrons do. There are certain things you can't make plastic do or glass do or factories do or robots do. And as you get into all these things designing a product is keeping 5,000 things in your brain, these concepts and fitting them all together and continuing to push to fit them together in new and different ways to get want you want. And every day you discover something new, that is a new problem or a new opportunity to fit these things together a little differently. And it's that process that is the magic."
Steve Jobs, Pioneer