I have a large kettle in which I can boil about 4.5 gallons of wort. After boiling the wort and chilling it, I dumped it into my carboy. My carboy has a mark on it to indicate 5 gallons. After dumping the wort in, the liquid level was about a half-gallon OVER the mark!!!!
I spent several minutes trying to figure out how I had made a gallon of liquid out of nothing. Maybe I had somehow acquired divine abilities. Sweet. What should I do first with my powers?
After thinking for a few minutes I realize what has happened. I didn't create matter. I forgot to dump the sanitizing solution out of the carboy.