You can tell how inexperienced Woo-Moon is by how he just kept attacking and attacking the Sandstorm forces, expecting identical results every time, as if the enemy was utterly incapable of learning from its mistakes. Furthermore, he was surprised the Muncheon bastards would be willing to have their subordinates carry poison on themselves, even though the Muncheon spies all carry suicide poison and are extremely willing to use it. Such noob mistakes. No matter how much of a genius Woo-Moon is, he's still very young and hasn't really had the time to learn to read and evaluate people, to predict what they might do and what sort of strategies enemies could be employing. The Palm Emperor also was kind of an idiot, so it's not like he would have taught any prudence to Woo-Moon.