Gaban told Luffy the secret to defeating immortality is to be mindful of the way he uses Conqueror’s Haki
I think he said this because Luffy an Zoro don’t know how to control the quantity of Conqueror’s they put into attacks. Zoro didn’t even know he could use Conquerors:
If his Conquerors isn’t tamed that implies he can’t control it well or at all. Kaidou also implied Luffy was still a novice with Conquerors.
Luffy’s control is probably better than Zoro’s, but still not perfect.
The reason this is important goes back to Roger and Garp’s discussion on Haki Mass. Luffy and Zoro need to be able to control their Conquerors good enough to put in enough mass to overcome Regen, but not too much to the point that they kill themselves.
I think he said this because Luffy an Zoro don’t know how to control the quantity of Conqueror’s they put into attacks. Zoro didn’t even know he could use Conquerors:
If his Conquerors isn’t tamed that implies he can’t control it well or at all. Kaidou also implied Luffy was still a novice with Conquerors.
Luffy’s control is probably better than Zoro’s, but still not perfect.
The reason this is important goes back to Roger and Garp’s discussion on Haki Mass. Luffy and Zoro need to be able to control their Conquerors good enough to put in enough mass to overcome Regen, but not too much to the point that they kill themselves.

