Where Do Those Ideas Come From?

I’m always surprised at the questions I’m asked when people discover I write mysteries.  How long does it take to write a novel?  How much time do you spend each day writing?  Where do you get your ideas?  Why write mysteries? Do you plan it all out ahead?  Do you outline the story first? How did you get started?
Answering the last question first, I think my four daughters got me started.  Instead of reading bedtime stories when they were very young I made up stories on the fly as they gathered together in their PJ’s just before bedtime.  It became a ritual and for some reason was easy for me.  I would ask them to name a subject, any subject, and I would make a story.  I remember one time they gave me hamburger as the subject and I made up a story about a hamburger whose lifelong ambition was to become a T bone steak.  I just let my imagination run wild.  Of course it helped that I had a very young and adoring audience.  I could do no wrong.  Sometimes I still do that when I’m writing.  I pretend I’m writing for a very young and adoring audience.  I’m allowed to make silly mistakes.
Maybe the most often asked question is “where do all those ideas come from?”   
Answer?  I force SITUATIONS, not the story, exactly the same way many mystery authors have done.  The situation dictates the story!
Example.  Perhaps the most famous example ever created is the much used “ locked room murder”  case.  The author puts the deceased inside a room with all doors and windows locked from the inside.  Now he has to solve that mystery.
Put your hero in an impossible situation and then figure out how to get him out.  Often the solution requires you to go back and make material changes in the previous work to justify your solution.  One thing leads to another. The story grows.  Yesterday dictates today.  Challenge your imagination.