This is a bit on the light-hearted side, but I once worked for a professor who
pronounced the Rule of Seven:
The number of years in school and the number of publications
must add up to seven: Four years and 3 papers, 5 years and
2 papers, six years and one paper, seven with none, or eight
years and a retraction.
The funny thing is, this has turned out somewhat to be true. He's had two
students graduate shortly after the end of their fourth years with at least
three papers each (1st or significant 2nd authorships), and he has one seventh
year with (I think) no first author publications.