Cheating
 

One day, while Sue was cleaning under the bed, she found a small box. Curious, she opened it and found 3 eggs and 10,000 dollars. A little bit suspicious, she confronted her husband of twenty years about it.
"Oh, that," Frank said. "Every time I cheated on you, I put an egg in this box." Sue was a bit unhappy about this, but figured that 3 affairs over twenty years wasn't so bad.
"But what about the 10,000 dollars?"
"Every time I got a dozen, I sold them."