The other day I was picking up breakfast from the deli for my family. I grabbed a Nestle vanilla milk for my son and waited for my order. The counter person packed my order, I paid and then I grabbed my bag and the Nestle chocalate milk on the counter and left. On the way home, I looked down and noticed that I must have grabbed someone else's chocolate milk from the counter as I left in addition to the vanilla milk that I paid for. Driving past my driveway, I turned around and went back. At the deli they laughed and said I shouldn't have bothered coming all the way back just to bring the chocolate milk.
A week or two earlier, I had been working replacing my deck. It involved at least a dozen total trips to the lumber yard. After returning from one of the trips, I realized that I had shorted myself three 8-foot 2x4's worth about $18 (the lumber people had seen me enough to trust that I could get the lumber myself). It wasn't a lot of money, but it was frustrating. I thought about telling them, but it would have looked shady. I thought about taking the 3 boards in one of my next runs, but merely the thought of being caught bothered me. Even though technically I had paid for them, and probably would not have gotten caught, just the thought of appearing dishonest was too much to risk.
I chalked it up as a lesson learned. I guess it is important not just to be honest, but to appear honest as well.