A minister, an artist, and a reservoir engineer were dining together, when the dinner conversation turned to the topic of women. It began when the artist proposed a toast, "To our wives and/or mistresses." The minister looked a little uncomfortable, and felt that he must state, not to be judgmental of course, that he would always be faithful to his wife.
"Nonsense," responded the artist. "Mistresses are preferable to wives in every way!" He then went on to wax poetic about how much better it was to be able to easily untie any knots and entanglements.
The minister, wanting to change the subject asked the engineer whether he felt a wife or a mistress was better. "I have both," the engineer responded quietly, "and I much prefer it that way."
Well, this stopped the conversation cold. When the minister recovered his composure he asked the engineer how this arrangement could possibly work.
"It's perfect," the engineer replied. "My wife thinks that I am with my mistress, my mistress thinks that I am with my wife, and I can go into the office and get some work done."