You do if you are a professional. I know the word integrity is not often associated with Charlie Nicholas, but I always remember his penalty in the 1990 cup final shoot out. Every single person on the pitch, in the stands and watching on tv knew he was almost certainly leaving Aberdeen to rejoin Celtic. If he missed then Celtic would win the cup. And yet he did the job his current employers were paying for and scored from the spot and Aberdeen eventually won the shoot out and the cup.
Although I was desperate for us to win that day, I would hate to have won if it was the direct result of him missing. The pressure he was under was immense as he knew millions of viewers were convinced he would do the dirty on his club. I admired him for his no nonsense goal that day. It is a pity he became such a bitter arsehole, but he was a brilliant player for us first time round.