The tip is to “break the glass” with every pitch.Here is how it works.
A pitcher visualizes a narrow rectangular box whose opening is right at the catchers knees like the picture above.The inside of the box is colored in the pitcher’s favorite color, we’ll say blue in this case.Covering the opening of the box is a plate of glass.On every pitch, the pitcher’s job is to break the glass meaning every pitch is down at the catcher’s/batter’s knees.Miss the box and you miss breaking the glass. I faded the photo of the catcher because if the pitcher is good at visualizing this, the catcher, batter, and umpire all become a blur. The only clear thing the pitcher sees is the location of the box and the glass in front of the opening.
With practice, a pitcher can visualize their box right at their catcher’s knees.When they lay in bed with their eyes closed, they can visualize breaking the glass with every pitch they throw.
It’s a great tip for some pitchers but it takes practice just like mechanics, grips, and footwork on bunt plays.