Recently, my guys were drilling back attacks and back defense in class.  There is a new kid that has been training with us for a month: he’s 16, about 6ft tall 230-240 lbs, trained at an affiliate school for an undetermined amount of time, and has been training with his buddies in his garage for a year or two.  He had his back taken and was trying to pry off the hooks with both of his hands.  I watched for a little bit and noticed he was fiddling with his opponent’s foot, like he was trying to attack a footlock.

I yelled at him, “Do not address his hooks with your hands.  You are leaving your neck out there.”(several times)
I yelled again, “Listen, run your back defense, whatever you learned on youtube or your garage is not working.”
He yelled back, “It’s working so far!”
He caught me off guard.
I replied, “ok we’ll see how well it works after class.”

I gave him a free private lesson for the next 1.5 hrs.  I told him to use whatever he learned on youtube or rolling around in his garage with his buddies on me.   Afterwards I explained to him, before he runs all the fancy shit he learned on youtube, he needs to shore up his fundamentals.  I promised him that all the guys he watches on youtube, they are all very very proficient at the fundamental movements and techniques of jiu jitsu.

I have nothing wrong with my students watching youtube searching for jiu jitsu techniques.  The problem is, these instructional videos are unregulated.  I don’t know if they are watching Marcelo Garcia, Keenan Cornelious, or Tom DeBlass(who happen to be my favorite videos) or watching some hack that’s obviously never trained BJJ in his life.  Obviously, he was watching someone neglect getting choked out or getting his arms trapped by someone’s legs running a back defense.

I’m old skool, my professor, Rob Kahn is straight up old skool.  I remember one time when I was a blue belt(2008 or 2009), he had Q&A in the Advanced class at Gracie Tampa.  I asked for him to show us a sweep, submission, or “something ninja” from bottom half.
He proceeded to tell us, “Get back to full guard or butterfly, half guard sucks.” LMFAO
He’s since relaxed a lot about some techniques, but that’s where I came from.  Fundamentals is your foundation.  Watch Roger Gracie vs Buchecha’s match in 2017.