User blog comment:Blackendedsoul/Difference/@comment-24769684-20150324215029

Well, I may get hate for this, but animals' minds are much simpler than ours. So while the elephant was physically stronger than Luffy, mentally it is much more simple and weak. As you've said below, it takes both mental and physical strength to resist Haki, and the elephant is completely on one side of the spectrum, while Usopp and Nami, while sort of weak physically, have the brains to back it up.