Your blog is great Steve, and practice is an interesting topic because as musicians it's the main thing we do.
Much like Stephen's "bloody-mindedness" comment above - I realized a while ago that I can wear down any difficult piece by just keeping at it. I refuse to go away and eventually it gives up and surrenders to me. I've learned to not rush past the hard parts. I slow right down, focus on playing the correct notes, if my fingering doesn't work I stop and methodically work out the best solution.
I used to play until I got to a mistake, then start again - that's an old and much discussed tactic. Or instead just gloss over the mistake and continue - making a mental note about the problem and thinking "I'll get that bit right next time". But it's been said that this teaches us to play the mistake. Each time we make the same mistake it's getting reinforced in our muscle memory. Instead, if I notice the same mistake cropping up I halt and think hard about what is causing the mistake, and think about the way to avoid that next. I might work on a single bar of music or phrase, ultra slow, fifty or a hundred times if necessary, gradually improving the speed.
There's also the saying "Don't practice until you get it right. Practice until you can't get it wrong".
I learned to have confidence in my subconscious musician. Our mind is very good at prioritizing skills if it sees them as important. If we practice every day in a focussed way, our subconscious says "hey, this must be important. I will devote extra energy to processing this." Equally, I've found sometimes that taking a break for a day or two from a piece means when I next come to work on it suddenly it's easier and I've made some progress - how can that happen without practice? Because the subconscious was working on it. Regular serious practice is a way of keeping the subconscious pump primed.
I used to play guitar a lot - eight hours a day was not unusual. Several times I decided to learn a piece I had heard and resolved to start the next day. But the night before I dreamed of playing it and working out the chords. The next day - yes, everything in the dream was correct, I knew the piece. If we know how to do something, we don't have to be consciously focusing on it for our brain to work on it.
The ten thousand hour rule (much debated) relates to world class mastery of an instrument or other skill. But, one hundred hours of serious and directed practice should get you to the point of being able to play some modest tunes on a new instrument, and a thousand hours to the point that you certainly don't sound like a beginner or dabbler any more. We don't have to become world class masters to play well enough to give ourselves and others pleasure.