This is one of the first really important lessons you learn in Brazilian Jiu Jitsu.
Everyone walks in, day one, and is dumping adrenaline everywhere they look. I mean, the person in front of you is literally engaging you in practicing murder, so I get it. Everyone starts that way. Super tense, super shallow breathing, and everyone wears themselves out in about 30-40 seconds. Of a 6 minute round.
Doesn’t matter if you’re the most insanely buff dude ever, or seriously overweight. The first guy has better conditioning, no doubt… but not this kind of conditioning. One of my favorite things was watching a new guy walk in, looking like he had maybe 7% body fat, 6’2” at least, plays D1 basketball, and is just nothing but stacked muscle… and then him rolling with a 5’6” 130lb woman who just wipes the floor with him, because training matters more than strength, but even more importantly, breathing and staying calm, slow, and smooth matters even more. The basketball player spends the first minute or so using all his strength to try and get this “puny” girl off of him, unable to, and is now completely gassed. Meanwhile she’s tapped him twice and could go for a run.
Eventually, the most important thing you learn is to relax and breathe. Technique eventually comes, through iteration and lots and lots of practice; eventually, things become second nature.
But breathing? Reminding yourself to relax and roll smart, not fast? That I need to remind myself of most days, because again: you’re facing someone practicing killing you. :)