Causality (also referred to as causation) is the relationship between an event (the cause) and a second event (the effect), where the second event is understood as a consequence of the first.
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If Ace's life wasn't in danger, they would've managed to get to FI.
Instead Luffy got his ass kicked in the war, concluded he was to weak to become pirate king back at Boa's place, AND THERE Rayleigh suggest to train more. Wow what a great idea.
Luffy and the rest of the strawhats would've been crushed like Gyro if they went to FI directly.
No discussion possible here
Luffy wouldn't be back at the Maiden Islands if he wasn't going to safe Ace !!!!
He wouldn't be breaking into Impel down, and he wouldn't go to the war.