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 - If you have a wife and a mistress, they will each assume you are spending time with the other woman, and then you can get some work done in the lab."