An architect, an artist and an engineer were discussing whether it was better to spend your time with a wife or a mistress.

The architect said he enjoyed time with his wife, building a solid foundation for an enduring relationship.

The artist said he enjoyed spending time with his mistress, because of the passion and the mystery he found there.

The engineer said, "I like both."

"Both?"

"Yeah," said the engineer. If you have a wife and a mistress, they will each assume you are spending time with the other, and you can go the lab and get some work done.