This was back when I was a teacher, but I organized a swimming carnival for an entire school. It took months of planning, and I really tried to design it so that it flowed well. It was a tremendous success ... and culminated in me reading out the winning team. The judges handed me the results on a piece of paper, but I was surrounded by lots of over-excited, screaming kids who were all trying to look over my shoulder to see the results, so I had to hold them very close to me chest. I was exhausted, and as I was announcing the results, I misread them, and announced the wrong team as winner.
Once I realized my mistake (with a feeling of horror I can't describe) I had to wait for all the screaming and cheering to die down before being able to correct myself—in front of hundreds of kid, parents, relatives, teachers, pool staff, and public onlookers. After all that work and planning over months (a lot of unpaid overtime) I was public enemy #1 for weeks, with aggrieved parents etc. complaining about me, damage control meetings etc... (Some felt I shouldn't have corrected myself, but I just couldn't do it to the real winners ...)
Not a single person said "well done" for the day as a whole. It was all forgotten.