The way that this shows that Odysseus is a good leader is that it forces him to make a really tough decision. Odysseus knows that he will need to sail very near the Scylla to avoid the Charybdis. He knows that if he does, some of his men will be killed by the monster. But he also knows that if he does not, all of his men will die because they will be sucked into the whirlpool.
