Out on a walk with my new girlfriend last night, only a small sliver of the moon was visible in the sky. She turned to me and asked, "Is it waxing or waning?"

I had no idea what to answer, but wanting to make a good impression I stopped and gazed for a few seconds wondering what the odds were I would pick the right answer of the two.

It was then that I realized there was a 50% chance of wane.