It just occurred to me that some of my readers may be unfamiliar with the concepts in my post on price ceilings. Supply and demand are basic concepts in economics, and although we all intuitively react to them in our daily lives, it's rarely a conscious thing. Public schools rarely teach economics, so I guess I shouldn't be surprised.
If a basic explanation of supply and demand confuses you, watch this video:
Rewind it a bunch of times if it goes by too quickly, and then try this interactive exercise (warning: it loads slowly).