The biggest ethical mistake I made was having a false sense of job security. I thought several people were my friends and I didnt realize how cut throat the office there was. My mouth ran when it shouldnt have, no secret there to anyone that knew me. My biggest mechanical mistake was a design for a gate that was air operated, and was actuated through steel cables. The cable fasteners were not good enough, they slipped, causing a loss in tension and an increased travel of the air cylinder. They were replaced over time.