To learning bjj and being good at it.
It's not about flexibility strength or stamina. It's nor even about number of techniques. It's about trusting your professor enough to do the moves he teaches you the way he teaches them when the situation he taught them for presents itself.
I watch white to black belts give up on techniques way too early, not try techniques when the opportunity is there and not complete the technique in the way or was taught. All because of fear and doubt.
If people let go of those their skills soar. It took me a long time to learn this. I tried to reinvent the wheel only to realize my coaches were right the whole time 
I was just thinking about this. GET OUT OF MY HEAD!
You gotta trust the technique or it will never work.
I think I do this. Some moves I learn and never use. Some I do use, but I probably don't use them correctly.
I tell myself that I am tweaking it to my style and just using what works for me, but then I think that every technique, as you mentioned, has a use.
This makes me feel like I am not retaining as much as I should.
I'm on a bit of a plateau right now. Stalled out if you will. Maybe it's just mental.
I think ego causes that more than trust. People are too afraid they might fail doing a new technique that they stick with their tried and true game.
I remember as a bluebelt training under an incredible halfguard master on a daily basis. What was I obsessed with at that time? Asking him for every detail that made him so awesome? Heck no, I wanted to become an expert in the turtle guard!
Now I have my own students. I have my own areas of expertise (relative to their skill level, at least), mainly butterfly, armdrags, and some other stuff mixed in.
Do they ever ask about moves I've been using every roll for 5-7 years? Nope, one guy with a year's experience wants to do spider guard and another decided he's going to be a rubber guard player.
I guess it's karma, and the nature of learning...
One of my friends always told me to trust in the move. It works. I can doubt myself, but have faith in the move, and the move will work. took me a while to understand it but once I comprehended what he was telling me, I started sweeping and hitting moved on guys I have no business hitting said moves on. Just had to figure out when to use them and when not to use them 
I found I did this alot, especially with moves that I had a misconception about (moves being for certain body types and all that). Once I got that outta my head it helped my game a ton. One of my favorite positions/subs was something I stayed away from at one point because I thought you needed a ton of strength for it (double wrist lock)
The concept of trust also needs to be extended to the training environment.
It's difficult to open up your game when you have to be worried about your partners fucking you up. It happens in a lot of gyms, even legitimately good ones. More people need to train with the principle of mutual benefit in mind.
This is why training women is easier than men.
They listen much better.
robhustle - I think ego causes that more than trust. People are too afraid they might fail doing a new technique that they stick with their tried and true game.Ego and trust go hand in hand. The student thinks they know better than the teacher so they don't change. That belief is based on a lack of trust of the teacher
SidRon - What if your professor is Ari?
I was just going to say that- you could end up trusting the wrong person and learning techniques that are either bad, or that dont work against higher level opponents.
this is very true. the other issue is trusting whether the teacher is being completely open and honest about all the details, and not hiding anything
So true as long as the Instructor is open with his/her students and really does have the student's best interests at heart!
kying418 -Then you'll be street readySidRon - What if your professor is Ari?
I was just going to say that- you could end up trusting the wrong person and learning techniques that are either bad, or that dont work against higher level opponents.