Depends on the player.
A combination of wilingness, ability to see the pitch out of the pitcher's hand (pick up spin), and baseball IQ to understand how to manage an AB.
ML club has gone from one of the smallest pitches per AB to one of the highest in one year, still a work in progress but they have changed.
Canelo is showing much better discipline, Tocci is not.
I think discipline is something they'll put a greater emphasis on in scouting.
It's not surprising that the undisciplined players are struggling in AAA ball, that's where you run into a lot of AAAA types with marginal FBs but good secondary pitches and command who nibble undisciplined hitters to death. Guys who can hit 95 MPH FBs will thrive in AA where you see a lot of kids throw hard without command or secondary pitches, but AAA is where they get exposed.
Interesting point with Pullin and Kingery, both are hitting much better on the road than at home, wonder if the weather this time of year blocks the winds that make Reading a hitter's park, and if that will change a month from now when the polar vortex moves out.