When I show people my paintings, the common question I'm asked is "what makes you think of these things?" There's a good chance that they're just being polite or making conversation, but if I indulge myself in that topic: An honest answer to that is that I'm not really thinking of them at all. A lot of what I paint isn't really there in the painting. There are huge zones of continuous color that don't contain much content at all.
But the other answer is that the world is kind of like that. The most interesting things are usually the things we can't see, because it makes us imagine. I always think a foggy day is the prettiest kind of day, and a lit window from the street is infinitely more appealing than whatever is actually inside that window.
I split my time between Seattle and San Francosco -- two very foggy places that leave a lot to the imagination. I think that's where my type of ideas come from.