Never Doing Conditioning
The first virtue in a soldier is endurance of fatigue; courage is only the second virtue. – Napolean
There are no blackbelts who never drilled. They just don’t exist. Repetition is your friend.
Avoiding new positions
Don’t learn new positions just to use them, but also to defend against them. Those who don’t use worm guard can still be swept by it.
Not Learning Break Falls
You only have one spinal cord. Spend the time to learn to defend it. “Protect yourself at all times” includes when you’re flying through the air.
Sticking to Your One Move
Having a submission at a high level is a great asset. Just don’t center your game around it. Your sparring can become one dimensional and predictable.
Only Training in Perfect Condition
Never stay home from practice because you’re sore or “hurt”. Let your injuries heal, but don’t let the normal knocks hold back your progression.
Counting Submissions or Taps
No one keeps score during class and neither should you. Most upper belts learn more from the classes where they do get submitted.
Emphasizing Youtube over Class
Youtube can’t watch you roll, provide feedback, or help you work through your gaps.
Not having a “move”
BJJ is a game of maximum skill and minimum skill. Aim to have a submission and pass that you trust against more advanced opponents. Just don’t overdo it.
Neglecting the basics
The basics are basic because they come up a lot and are essential, not because they are easily mastered.
Never Starting from the Feet
If you care at all about BJJ’s self-defense aspects you should probably care about the position where 100% of all altercations start.