In dutch there is this saying.
Een ezel stoot zich nooit tweemaal aan dezelfde steen.
A literal translation would go like this.
A donkey never bumps into the same stone twice.
Even a donkey does not bump himself twice against the same stone…
A less literal translation would be this.
Fool me once, shame on you. fool me twice, shame on me.
So unit testing is all about being the donkey or the fool or both ;-).