Just prior to the final battle, Egg Shen gives Jack, Wang Chi, and the rest of the Chang Sings a magic potion.
The potion gives them all extreme confidence, and also tremendously boosts the fighting powers of all but Jack. Wang Chi is even able to match the skills and abilities of one of the Storms.
However, aside from the confidence boost, all the potion seems to allow Jack to do is
catch a thrown knife and throw it back quickly
While this is somewhat impressive, we are left with the impression that this is almost as much luck as skill, since
His first throw with the knife misses horribly.
Why did Jack get much less of an effect from the potion than everyone else?