An architect, an artist and an engineer were discussing whether
it was better to spend time with the 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 time with his mistress,because of the passion and mystery
he found there. The engineer said, "I like both."

"Both?"

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