I've been teaching a lot lately.
Oddly, I've been using "Dancing With the Stars" as a metaphor. When you watch the pro, you see each motion extended to its fullest. Each step is precise; exaggerated, even. The legs are long, the toes are pointed, the necks are arched just so.
With the amateur, there's a degree of uncertainty. Incomplete fulfillment. The envelope is not pushed.
I had a young lady playing some tango duets with me, and it was adequate. Accurate, possibly. But exciting? Not hardly. Then I tossed out the phrase "self-destructively beautiful." You know those people, right? The ones you just KNOW will go up in flames. They can't keep up that level of intensity.
When she played the piece again, it was ravishing. Her heart was on her sleeve, and she went so far beyond what was on the page, she was shredding the paper (metaphorically). I felt like I heard her heart beat in her sound. I did not tell her quite how I felt (I almost teared up) for fear of freaking her out and making her feel weird. But wow.
Later the same week, I tried the same description with an adult student of mine. There is this point in Debussy's Syrinx, where the story goes off the rails. Madness. Ecstasy. Dangerous, self-immolating beauty. After that point, the music is just like ashes and smoke. It burnt itself up, and now it's just ... dying. It's the beautiful afterimage etched into your eyes from glancing directly at the sun.
You can only see it when you close your eyes.