Einstein's theoretical work was thoroughly incomprehensible to his second wife, Elsa:
"Could you tell me a little about your work," said she. "People talk about it and I am so stupid, all I can say is that I know nothing."
Einstein thought, then frowned deeply as he pondered how to begin. At last he spoke:
"When people ask you about my work, tell them you know all about it, but that you can tell them, as it is a great secret ..."