The overconfidence of youth with none of the discipline martial arts should teach. Seems like a justifiable outcome.
I took karate classes when I was about 11, but I always had the lingering sense it wasn't preparing me for real self-defense. When I was in teens, I joined the Young Marines and learned a bit of Marine Corps Line Drill. I saw similarities in the stance, but a world of difference in the applicability.
I'm glad to say I have avoided armed and unarmed combat successfully so far.