The usual robot related stuff like over valuing the ability to cap an existing six stack with an RC that made our robot a jack of all trades and master of none.
While I was mentoring a team I really regret losing focus on what this is all about. Having a competitive spirit is good and winning can lead to inspiration on its own, but that competitive side can really put a damper on the ability to work with students. There's a thread that usually comes around every once and a while about mentoring fresh out of high school. If you decide to take that road (and let's keep that discussion in those threads), really ask yourself and more experienced mentors/adults around you, "How can I be a better mentor for the students?" I wish I did.
Regardless. Learn and move on. You can never take something back or go back in time. Consider how you can prevent it from happening moving forward and remember those mistakes when you come across similar circumstances.