I believe everybody has the capability to create one good piece of art in as many fields in which they have an interest. Not two good pieces... but probably one in many different fields.
Even though we're not all song writers, painters or industrial designers. I think that we all have it in us to create one good thing in all those fields. That is, if they are of interest to us to start with. If something is interesting to us we think about it in more details and we have a precise mental picture of what the 'best' is for that subject. Let's take song writing as an example. For most of us, since it's just an interest (as opposition to a passion) we don't work in that field and so for years we just roll around that one image of what makes a good song, and the best styles and the kind of subjects we like. We might even catch ourself thinking how cool it would be to hear more songs fitting that bill. So if at a given moment somebody was to ask us “Can you write me lyrics for a good song.” we could say “Yes! I have the perfect song.”. And than the flood gates would open and we would put that song on paper in no time, injecting in it every ideas we've ever had about what would make a good song.
It would, most probably, be our only song. At least for quite some times. This is because all we had went in that one song and we're left with nothing to create a different one.
I could probably ask anybody to design a good cell-phone interface and (if they use cells) they would all have a pretty finite idea on the perfect size, color, finish, button shape and many other details. It's all cool but can they design ten new phones every years? My guess is no. Of course the world is full of exceptions so there are people good at everything and others that couldn't make anything good in fields they love.
Mental pictures let the designer in us give a shot a everything. Unless we actively work at it, I think our 'inner-designer' only works on one concept which is 'the coolest' (for us). Once that concept is used... the tank is empty.