Thought I´d get the ball rolling for some laughs.
When running a trade route between A and C jumping via B I was very confused when I all of a sudden would sell my goods at a loss. I wondered how the heck the prices could have gone down so dramatically and decided to go back to where I bought and off-load there for a hopefully smaller loss and then look for a new trade route. I jump out to "C" and onwards and suddenly find that I´ll now sell the stuff with a good profit. Finally the ball drops and I realise that I obviously jumped from A to C and back to A initially. Doh! Would have been an even more senior moment if I´d actually had sold the stuff at A (thinking I was at C) instead of deciding to go back to what I thought was the place I had bought the stuff. Too old, too late.
Lessons learned: know where you are, write down the end points and what goods should be sold/bought at each place, drink more Kilkenny (always true).