A great detective is a master of observation: he remembers details, connects the dots, uncovers motives, and draws conclusions. Such is also the responsibility of the performer regarding the interpretation of the score.
Music emerges from the score like a tree from the ground: same seed, same elements, same principles, same basic laws, same holy trinity, same universe, but infinite permutations. All trees are created equal and yet no two trees are the same. That applies also to a performance of a piece. Understanding the fundamental principles gives fertile ground and deep roots for a fruitful interpretation.
When Chopin writes pianissimo, he doesn't mean your pianissimo, he means his pianissimo.
And when he writes pianissimmissimo and delicatissimo ... one can only hope and dream to imagine what he meant.
The unlimited fascination of music emerges from the superposition of multiple levels of organization and information.
The acceptance of ambiguity, due to that superposition of multiple levels of organization and information, is a key to music interpretation.
You have to use not only common sense but also vague intuition, not only knowledge and tradition but also personal inclination and inspiration.
Instead of asking what "the music is about" in the first page of Liszt's Sonata in b minor, i. e. searching inspiration from thematic connotations and programmatic narrative (Milton or Faust or Bible ...), I find it much more relevant and revealing to contemplate: how would Liszt orchestrate the score?
And it seems apparent to me: timpani, strings, brass, and wood winds - all instruments of the grand orchestra in the first page alone. Later in the Sonata there are sounds of organ and harp, thunder and howling, celestial and percussive sounds, as well as voice - choir, song, aria, and recitativo -, and even the grand piano.
Dynamical markings such as Forte and Piano are expressions of character and quality, not positions of a HiFi volume knob.
Crescendo, which means growing, suggests development towards higher expectation. It does not necessarily mean development to Forte, which means strong, but can also suggest development within Piano, which means gentle.
Die Meinung, im Barocken und auch im Klassischen Stil Verzierungen hinzufügen zu dürfen, ist oft vertreten; aber man spricht nie davon geschriebene Verzierung - embellishments - wegzulassen wenn sie ihre Rolle nicht erfüllen und zu Verhässlichungen - enugliments - werden.
Paul Badura-Skoda, IPAF11
In polyphonic music it is imperative to play the subjects (themes) at the dynamic level of their natural vocal positions in relation to the counter-subject (counterpoint) and not bellow them above the background of the other voices. There is no background: Polyphony is the equality of voices.
One has to wonder why publishers of Urtext editions, for example Henle, hired experts to provide fingerings when the composer's Urtext didn't include any.
Fingerings were (and should be) taught as principles, not isolated instructions, and composers only marked fingerings in their scores when there was an urgent reason i.e. a particular expressive articulation and/or an innovative pianistic idea. The fingerings of composers worked well for their hand on their instruments and need to be interpreted - like all musical notation - in context.