Both lifters try to pull too far and too high on vertical pulling motions such as pull-ups and lat pulldowns. Rather than trying to touch the bar to your chest or reaching your chin over the bar (both of which can produce dysfunctional mechanics), the goal should be to achieve proper upper back and lat activation.
Sometimes it's really interesting to dig into the microscopic details of training and nutrition, to dissect the body of academia and examine every little study. That's how we learn things. That's how we refine the science that later helps us get bigger and stronger and leaner.