There is a point in a musician's development when the music because internalized. That is a kinda vague description but it is roughly the time when "you get it". You aren't just playing the notes or your part, you are part of the whole and you can figure out where your part fits and how. In an orchestra it works kinda like this: The conductor is the general interpreter; somewhat of the glue that binds the book. The music is, well it is the print on the page and everyone who plays the piece encounters it the same way as notes and musical symbols. It looks exactly the same in any location on earth no matter the country or the language (hence music being, like math, a universal language). The musician reads the book along with all the other musicians in such a way as to stay together with everyone else but also to put his/her own stamp on the passages (their own expression) and keep with the conductor. It is complicated...but you will know it when you see it and particularly when you hear it. For example: