iternabe practicing at tempo well below one's own threshold does little to help gaining speed
I just don't agree with this. There is much more to increasing the tempo than not making too many errors. It's important to figure out where you're making the errors, and most importantly why. Playing very slowly will reveal the errors much more clearly. Is it about not knowing the notes well enough yet? Would a different fingering help? Is there any other kind of distraction there, like dynamics that haven't been fully internalized? Is it a matter of rotation, or needing to push out more from the fallboard to prevent tangling with black keys? Is it faulty rhythm? Once the problems are diagnosed and solved, then clicking up into an increasingly challenging tempo seems to be the most popular choice among the bazillion YouTube videos I watch looking for ideas.
I would love to see one piano teacher in a video saying, Just play a bit faster, and you'll get there eventually. I don't believe there is one, and if there is, I wouldn't want to follow advice that contradicts so much other advice.
I have the sense, @iternabe, that you already know all of this, and you mean that after you've slowed down, and found and fixed problems, that at point, it's time to push the envelope. I agree with that wholeheartedly.
