They say necessity is the mother of invention. I developed a to-do list accidently. Years ago, I started keeping track of what money my roommates owed me from month to month. To make sure we all knew, I started writing it on the bathroom mirror with a dry-erase marker. Soon we were leaving each other notes like "Went to see a movie, be back at 6pm." Then it became a running list for food shopping. Now, even though I live alone, I still use that technique to keep myself organized. It's much easier to lose a sticky note than it is to lose the whole bathroom! Now I just need a mirror on my desk at work...