There isn’t just one person in the practice room or on the stage when one performs. There are two people there: the performer and composer.
A unique collaboration happens when you perform another’s work. You are taking the musical ideas of a Mozart sonata and transport it through the lens of “you”.
It’s as if the 21st century you and the 19th century Mozart are having a conversation as you learn the piece. It’s as if you both are writing the piece together. What an unlikely partnership!
You’ll both agree and disagree. Sometimes you’ll have ideas of phrasing that Mozart didn’t have in mind.
And that’s okay. You two can discuss it.