@maisonaustyn They have all of the reasons to be full of themselves. Their state was the first one to declare itself a kingdom when Zhou dynasty was still around, they managed to survive against Sun Tzu and after that managed to take out the state of Wu which Sun Tzu served, they had several military geniuses likes of Wu Qi and Lu Ban ( Gongshu Ban) the former who wrote war treaty Wuzi one of the seven military classics of ancient china and considered to be an equal of Sun Tzu's art of war, and the latter who today is considered the god of military engineering.
Oh and even tho this will only become after the unification, a general from Chu Xiang Yu was considered the strongest man of all china who once with the only a force of 30k won against a massive army of 500k. So yeah they are wholly justified to be cocky.