Say you are dying to bake something and are craving something chocolately, something cakey... maybe a chocolate cookie? You inventory your ingredients and think you can do it, but have no specific recipe in mind. The perfect cookie in your head hasn't been baked yet, and baking is a delicate and exacting science of carefuly tested proportions and measurements. You realize you don't even have a measuring cup or a cookbook on hand. But you want This Cookie. You're a rebel. You've baked cookies since you were knee-high. You can do this! You go for it.
The cookie you produce is utter perfection: a beautiful pillow of chocolately goodness! This would be a perfect ending to that dinner you were planning... maybe next time topped with a chocolate ganache and some chopped walnuts for texture... and oh, crap. Did you write anything you did down? Measurements? Baking time? Nothing? Good job, Slick. By not writing anything down, you've ensured that the secret to your successful experiment will remain a secret forever.
Lesson learned: If you ever want to repeat a success when you're playing in the kitchen, write down what you're doing while you're doing it.