So, when I was growing up I had two older brothers, and they were bigger, meaner, and smarter than me. This is not a wonderful equation to live under.
For sport, they would throw bean bag chairs on top of me and sit on them. For them, it was great fun, for me, it was horrifying. I remember vividly not being able to breathe well. I could still yell out "MOM! I CANT BREATHE!" and my mom, being typical old school would reply "If you can yell, you can breathe.". Long story short, I dont remember dying. May have happened, and I am not in some form of perpetual hell that I cant escape, and you are all here with me, or are figments of my hellish nightmare.
With that said, I really, honestly, and truthfully could not breathe >well< and if my brothers had continued to apply the pressure I have little doubt I would have passed out. They had applied pressure to my abdomen which made breathing exponentially more difficult. With effort I could breathe, but at perhaps 20% capacity. Enough to make wimpish yells for aid, but not enough to completely sustain myself. My brothers, being the experts in anatomy as they were, knew to jump up every time my mom would yell at them to cut it out, just to flop right back down on top of the bean bag chair and exclaim "I did get up! I did get up!".
So, I do understand that "If you can yell, you can breathe" is only really partially true. You can breathe, but not enough.