A farmer just got married and was going home on his wagon pulled by a team of horses. When one of the hoses stumbled, he said, "That's once."
Then it stumbled again. He said, "That's twice."
Then later it stumbled a third time. This time, he didn't say anything, just pulled out a shotgun and shot the horse dead.
His wife cried out and started to yell at him. The farmer turned to her and said, "That's once."