What are the sources of ideas?

From Revising Fiction by David Madden:

"'Where do your ideas for fiction come from?' writers are often asked. Here are a few typical answers:

1. My own direct experience — what I have done or what has happened to me. (At work here is the autobiographical impulse, which sometimes becomes a compulsion.)
2. Experiences of strangers or friends that I have only observed, or have been told about as stories.
   
3. Actual events reported in newspapers and sometimes on television.
4. Notions or concepts or images for stories that my reading in fiction and poetry, or my viewing of movies and plays, stimulates.
   
5. Experiences that well up suddenly out of my subconscious.
6. Experiences that I willfully and deliberately conjure up out of my imagination — experiences that I see and feel only in my imagination. (Beginning writers have great trouble imagining stories.)
7. Publisher's ideas — a novel about white collar crime, for example.
   
8. Ideas from my friends and relatives.
9. Ideas suggested by dreams.
10. Possibilities posed by a new or different technique. (One then imagines uses of that technique.)

Once a writer has a story, he may make a short note, file it away, turn it over to his creative subconscious, and wait for the day — perhaps five years later — when the compulsion to tell that story takes possession of him."

Assignment: (From Fiction Writer's Workshop by Josip Novakovich) "One page . . . Write a scene of a story from a glimpse you have had of a group of people — in a cafe, zoo, train or anywhere. Sketch the characters in their setting and let interact. Do you find that you know too little? Can you make up enough — or import from other experiences — to fill the empty canvas?

Objective: To find out if you can make much out of little. If you can, great, If you can't now, don't worry, you might later, or you'll have to get your stories from other materials.

Check: Can you visualize these people further? Can you begin to hear at least one person speak? If not, go back and find a way of talking that might fit one of the people in this group, and carry on from there."