On the video you see her withdrawing her shoulders. The first bars of the d-minor piano concerto by Wolfgang Amadeus Mozart are sounding. Pires, whose facial expressions embody different emotions at the same time - from shame over to desperation to decisive - rests her head on her arm at the piano. She looks up to the conductor. "I'm going to try", she says.

The conductor is Riccardo Chailly, and the orchestra is Concertgebouw Orkest Amsterdam. We're in Vienna, at an informal lunch concert.

Upon hearing the very first note, Maria João Pires has realized that she prepared the wrong Mozart concerto. The music sounds, the audience awaits.

And she is not prepared.

How could this happen? When this anecdote was made public, there were comments about it not being usual to rehearse before a lunch concert, about it looking more as a public dress rehearsal (Chailly has a towel around his shoulders), and that, for whatever reason, there was no previous contact between conductor and soloist, not even on the phone, to discuss the piece. There, they would have realized that they were talking about a different Mozart.

But that wasn't, and now we're at Wiener Musikverein, and the orchestra is developing the main theme. And here is Pires, who is trying to get around to the idea that she's going to have to play a 25 minute piece that she hasn't prepared.

On the video, Chailly looks at her from the podium.

Her: "I had another concerto in my schedule…"

Chailly: "This one you played last season." He smiles. "I'm sure you can do it. And you can do it well."

Meanwhile, the orchestra is already playing the secondary theme.

The video is an excerpt from a documentary feature about Riccardo Chailly and the Concertgebouw Orkest, and the scene is commented by Chailly himself.

Fascinated by the reactivity of the pianist, he describes enthusiastically how she could switch in one minute to the other concerto (the orchestral prelude takes no longer than 3 minutes), and play it without even one false note.

Back to the concert. The orchestral prelude is finding its ending. The orchestra reaches the coda and Pires prepares for her first entrance.

The orchestra delivers to the pianist its last sound. And Maria João Pires begins to play.

And then, the miracle. In the very first bars, one sound leads to the next one. Her commitment… it just takes my breath away.

The luminosity in her sound.

I'm deeply moved.

This anecdote from 1997 is one of the most fascinating, because at the same time it's one of the most horrifying. Imagine that you go to play a concert and you prepared the wrong piece.

A few years ago, this story was picked up by the internet and widely spread. There was talk about the miracle, about the pianist's ability to concentrate, about her powers of recollection, and about how she could remember every note of the piece without playing one single wrong note. Even though she hadn't prepared the piece. Even Chailly says it in the video.

But what nobody was commenting on (nobody except for Stephen Hough, whose article isn't available on the net anymore) was this glowing richness in her sound, her complete surrender to the moment, in which the piece unfolds, her surrender to the music.

In these moments, we see how emotion turns into sound - the most authentic way to express oneself musically.

The miracle is not about playing all the right notes of the concerto. It's obviously a piece in her repertoire. For her, one or two days of practice would have been more than enough.

The real miracle happens because Pires knows that in the moment she decides "I'm going to try", without knowing if her fingers will remember, that she recognizes that her task is to move as close to the sound and the music as possible, and to play the concerto on this basis.

This story shows in the most radical way the importance of the inner, emotional preparation: to feel and understand a piece from inside, to turn the piece into your piece.

The external preparation - of the fingers, of the pure movements - can lead to a performance that is apparently perfect and flawless.

But the artists that really move us don't do it because their performance is perfect and flawless. They move us because they are authentic, present in the moment, and they achieve this by preparing the piece always connecting to its emotional content, by preparing internally, and by training themselves to move this emotion through their body from the inside out. Then, emotion turns into sound and reaches listeners' ears. And that's what moves us.

Because emotion leads to precision, and not the other way round.