Most aspiring musicians take ten times longer than necessary to learn a piece of music for this one reason.
They play before they think.
It's not their fault. Modern culture has made us this way. We love fast. We love instant. We want to get things done quickly.
The idea of slowing down to accomplish things faster is not intuitive at all.
A week or so ago, a student was playing a passage over and over again with mistakes. In the same places. Every. Time.
Once I got him to stop playing, I said, "Take a few seconds, figure out where the mistakes are happening, figure out how to fix it, and then play."
His response? He started playing again.
"No, don't play!! I said figure out what you're fixing first!"
Sensing I may spontaneously combust at any moment, he took the twenty seconds to look at the music and figure out what was going on. There were two hand position shifts he was missing.
"Okay, got it." And he played it flawlessly on the next rep.
Eureka!
Think for a minute (or even several minutes), and play once.
Don't be like everyone else who plays fifty times and thinks about what's for dinner tonight.
Think before you play. It might sound a bit too simple.
But the simplest tactic is often the most successful one.