One year I had a plan to put a "Welcome Santa!" sign in front of the fireplace in a way that it would have to be torn by Santa to get into the house. If I woke up and the sign was torn, then Santa was real and he came.

Unfortunately, I made the mistake of trusting my parents and telling them my brilliant plan. Needless to say, the sign was torn even though Santa never actually came :-(

Little did I know that this was the beginning of a lifetime of intractable skepticism