Mistakes can easily happen. I recently fell foul of security at a UK airport. In my haversack they (found by scanning the bag) a very small bottle of hand sanitiser. It was under the base flap of the bag, which is only secured on one edge so the bag folds up when not in use. I had no idea it was there. It was allowed to be taken on the flight because it was below 100ml, but it should have been in the mandatory plastic bag. I had even collected a couple of plastic bags from the stand prior to checking in, in case we needed them later. The last time the bag was in use my daughter had borrowed it for a long distance walking expedition (Nijmegen Marches, last summer). I accepted the bollocking and apologised.