How strong-willed is Odysseus? Think about Circe's advice for the Sirens.
I suppose you can say that this shows that Odysseus is strong willed because he is willing to undergo this really severe temptation since it is the only way that he will be able to keep his men safe. This shows a strong will because he is willingly undergoing what must be something like torture.
Odysseus is going to have himself tied to the mast so that he cannot move as he hears the song of the Sirens. While he is tied to the mast, he will be hearing this song that is so compelling that it makes men go to their deaths. So he is voluntarily undergoing this torture -- he will listen to this song that is so tempting but he will be unable to do anything about it. It takes a strong will to undergo something like that.
I see a strong will in Odysseus in many places. However, I am not sure that the Sirens scenario demonstrates strong will. Rather, I see selfishness. If you are tied up, and you have instructed people to tie it tighter if you ask to be removed from the situation, I think that shows you do not have a strong enough will to overcome a worthy foe or problem.
These Sirens are a delicious and pleasureful sound that he does not want to miss. His selfishness (yes, at Circe's advice) leads him to listen to the their hauntingly attractive song.