rep speed and mind muscle connection mostly
I had to take 90lbs off when I slowed down my reps and stopped dead at the bottom, also keeping your spine flat, no buttwink is limiting on the weight you can use (99% of people don't give a fuck about this, but I have 4 blown out discs from being a fat retard PowerBuilder when younger)
I squatted 405 for 10 a couple months back quite fast reps, I got barely 3 reps with that weight and perfect BBing form at the same depth.
when I see bullshitters here talking about how 405 x 8 is nothing, can be done after just doing Jump Rope for leg training, I