Grandpa Cartnell was celebrating his 100th birthday and everybody complimented him on how athletic and well-preserved he appeared.

"I will tell you the secret of my success," he cackled. 

"My wife and I were married 75 years ago.  On our wedding night, we made a solemn pledge.  Whenever we had a fight, the one who was proved wrong would go outside and take a walk."

"Gentlemen, I have been walking in the open air day after day for some 75 years now."