At slow, manageable tempos, you can afford to use motions that don't scale to fast tempos. If you only ever play "what you can manage" with meticulous, tiny BPM increments, you'll never have to take the leap of faith and most likely will hit a wall, never getting past like 120-130 BPM 16ths comfortably. Don't ask how I know this.
What got me past that point was short bursts at BPMs way past my comfort zone and building synchrony _after_ I stumbled upon more efficient motions that scaled. IIRC, this is what Shawn Lane advocated as well.
I recommend checking out Troy Grady's (Cracking The Code) videos on YouTube if you're interested in guitar speed picking. Troy's content has cleared up many myths with an evidence-based approach and helped me get past the invisible wall. He recently uploaded a video pertaining to this very topic[0].
This is actually pretty close to what Stetina says. I just probably didn’t do a good job expressing it.
You’re oscillating above and below the comfort zone and that iteration like you say affords insights from both sides, and eventually the threshold grows.
Great suggestion of a video, I’ll check it out.
His method was to play alongside the student at 100x their skill level, pushing against their idea that it was too difficult.
But they’d play it, at tempo, horribly, from beginning to end. And then zoom in to a section and begin improving a few phrases at a time.
It was wild to watch, because after months of this, my 11yo could do something that seemed impossible.
It seems like this is a far more time efficient methodology to build speed on guitar, I do not know why it wouldn’t apply to other instruments like trumpet.
I guess I'm agreeing while also saying that you can get there by failing a lot at full speed first. Maybe he practiced at half-speed when he was alone and I never saw that part.
I think this post only covers one side of the coin. Sure, getting things done fast achieves the outcome, but in the long run you retain and learn less. Learning new stuff takes time and effort.
When you practice your instrument you get better att doing the exact same things the sloppy player is doing, but you do it in time and in tune.
When you get faster at building software by (ostensibly) focusing on quality you do not do the same thing as someone that focuses on quick results.
It depends on the level we look at it, but I think there is fundamental difference in what excellent (professional grade?)players are doing compared to "sloppy" ones.
It is not just done with more precision and care, they will usually have a different mental model of what they're doing, and the means to achieve the better result is also not linear. Good form will give good results, but it won't lead to a professional level result. You'll need to reinvent how you apply the theory to your exact body, the exact instrument in your hand, what you can do and can't and adjust from there.
That's where veteran players are still stellar while you'd assume they don't have the muscle and precision a younger player obviously has.
PS: I left aside the obvious: playing in time and in tune is one thing, conveying an emotion is another. It is considerably hard to move from the former to the latter.
After a certain, moderate level of skill, all musicians hit the notes. That's not what differentiates them, and they're not playing the same way.