Why is this so relevant? Because during the Whiskey Peak Arc he came to doubt Zoro because of the words of wounded man, and even doubted Robin during Water 7 before Nami told the crew the truth behind Robin’s desertion. But not even once he doubted Nami :O
What does this have to do with Strong World?
After listening to most of Nami’s recorded message, Luffy gets enraged! Why? The theory: Luffy never doubted Nami, he always relied on her blindly putting his faith in his navigator, to an extent greater than his trust in Zoro or Robin. So after thinking his navigator doubts him and his capabilities he got really angry…