more piano appreciation from a very amateur pianist:
every piano is different. unlike a viola, you cannot carry your instrument with you. unless you have one at home, you don't have your own instrument, and if you're at school most of the time, you'll be using many different pianos based on what's available in the practice rooms.
because of the above, you have to adjust to every single different piano you play. they respond differently depending on the weight of the keys and probably a billion other things i haven't even noticed. whether it's got sticky keys. whether it just Sucks. i still can't even tell super well when a piano sucks but i sort of can.
the piano is basically a percussion instrument, making the above point quite relevant. my friend likes to say it's kind of an instrument of illusion. the sound disappears as soon as you hit the key (unless sustain pedal, but that's a whole other point), so how do you create phrases? how do you distinguish lines and voices in the music? how do you create music? and how do you do any of that when every piano responds a little or a lot differently?
piano music often has many voices at once. you gotta make them all sound right, make sure which ones are the focus and which ones aren't. it's not only a matter of coordination as far as hitting the right keys and notes, but also which ones sound more than others, which ones to linger on, which ones to press slightly harder to make a particular line come out.
Pianos Have Pedals. As In Foot Pedals. More Pedals Than A Car (unless it's a manual, lol). you coordinate not only your hands, but your feet. and actually, more like your arms and your legs. and actually, more like your whole damn body cuz it's all one body that's attached and if you want to maintain it for any amount of time you MUST play in a way that is healthy for your whole body.
a lot of this is just poetical phrasing of what pianists work on when they practice, and again, i'm not a pianist and i could be missing or mistaking or misunderstanding a million different things about this instrument, but this is what i've gathered from my own experience sort of learning on my own and with the help of some friends. appreciate your local pianist 👍🏼 and if you don't have a local pianist, all the pianists in the universe 🫶🏼