The linked article says:
While that is true most of the time, it is absolutely not true all of the time. Whenever a person has difficulty racking a slide, they need to recognize whether they are unable to pull the slide back or are unable to grip the slide enough to pull the slide back.
After my wife had hand surgery, she complained that she could not rack most pistol slides. I reminded her about the correct technique (she was an experienced shooter) but she still insisted she could not rack the slides. In my arrogance, I decided she was simply not trying hard enough to apply the proper technique. Then, fate intervened to teach me humility.
I injured my left arm in a way that seemed very minor, but I hurt the ulnar nerve in that arm. I quickly lost grip strength in my hand, to the extent that I could not maintain a grip on to a 12-oz. soft drink can. After visiting my doctor, my wife said something about maybe now I could understand what she had been trying to tell me about her inability to rack slides.
I went to the gun safe, pulled out a pistol and was unable to rack the slide. Oh, I knew the technique and had plenty of muscle strength to push and pull on the frame and slide. In fact, I had enough of that muscle strength to easily jerk the slide cleanly out of my grip. What I did not have was the grip strength necessary to maintain a hold on the slide.
My ulnar nerve healed and my loss of grip strength was temporary. Unfortunately, some people have permanent loss of grip strength which makes it difficult or impossible to rack slides using the techniques that work for the majority of us.