Odysseus didn't want his crew to freak out nor find out that they were gonna face Scylla. I'm pretty sure that he keeps it a secret and about half of his crew die.
He had 2 choices: Lose every member of the crew, or lose half of them. Odysseus made the wise choice of choosing half.
I'm 83% sure, because that's the story i was told/interpreted. So, hope that helps!
