A mother was cooking a joint of meat for her family. She cut off a large slice from the side of the joint, then put both pieces into the gravy.
“Why are you doing that?” her daughter asked.
“It helps it cook properly. That’s the way my mother always did it,” the mother replied.
“Why does it help?”
“I don’t know. Maybe I’ll ask your grandmother next time I phone her.”
So the mother phoned the grandmother. “Why do you always cut a slice of meat from the side when you cook the joint?” she asked.
“It helps it cook properly,” said the grandmother.
“I don’t know. It’s just the way my mother taught me to do it. Maybe we should ask her why!”
So the family went to see the elderly great-grandmother. “Why do we always cut a piece of meat from the side of the joint, before we put it in the sauce?” the mother asked.
“You still do that?” the old lady laughed. “I love you, and love that you trust in what I do, but you should find your own way to cook. I did it because it was the only way it would fit in my pot!”
(My father told me this story when I was a child; apparently it appears in “Surely you’re joking, Mr Feynman” by Richard Feynman.)