I GM "on-the-fly". I set up the situation and give players options. If they do something dfferent than options given, I go with that. I have nothing in writting nor do I know what's going to happen next until player's tell me what their actions are and/or roll of the dice then I react accordingly. When next session rolls around I pick up where we left off and what we did; all from memory. It's kind of like all those sports guys who remember every little detail about stats and games. And I have 3-4 different games going at times. All on-the-fly.
Then my wife gets mad at me because I forgot to pick up milk and bread on the way home.
![Big Grin :D](./images/smilies/biggrin.gif)