I don't really know that I'd say it was due to overconfidence so much as him being the only one that even played like service to their plan of drawing out the fights and then getting caught off guard by his opponent's choice to commit suicide rather than be killed by Vegeta when he spared its life.
Honestly, all the human fighters, especially Yamcha, are essentially the equivalent of Naruto's Sakura Haruno, in that they are hard working geniuses who just happen to end up hanging around people who work at least as hard as themselves, are also geniuses, and also have a bunch of broken abilities that they are born with which give them arbitrary massive power boosts whenever it is convenient to the plot. I'm hoping that one of the humans figure out how to use God Ki and/or Ultra Instinct and essentially close the difference.
Last edited by The Drunkard Kid; 02-19-2019 at 09:54 PM.
Critics who treat adult as a term of approval, instead of as a merely descriptive term, cannot be adult themselves. To be concerned about being grown up, to admire the grown up because it is grown up, to blush at the suspicion of being childish; these things are the marks of childhood and adolescence.
- C.S. Lewis
His back was turned after a decisive victory over the Saibaman. He was confident. It wasn't unearned or unjustified confidence mind you (that's the difference between confidence and overconfidence; nor did I say he was overconfident, but that's splitting hairs), but it did mean lowering his guard because no one expected the Saiyans and the Saibamen to take it that far.