One of the biggest challenges of all is knowing how to stay physically connected to a long note, in such a way as to make the task of connecting the next note (both physically and musically) as easy as possible. Instead, they tend to be stiff or go flaccid and totally lose the physical connection to the sound. There's a lot of technique in connecting a long note to the next.
Yes, absolutely, and this is the kind of thing I am working on (with good guidance). On piano, a note will sound only if the damper is kept off the string, which is done either by keeping the key depressed, or through pedaling. The "piano key" way is the first thing we learn.For legato playing, we want note 1 to sound and only to stop sounding at the moment that note 2 is played maybe with a titch of a blend. So you are holding the key
down until you press the next key
down but around that point the first key has to go
up, all with fingers attached to the same hand, and arm mechanism. Between the ups and downs you can have a conflict.
Then there is the fact that while you are holding a key down for a long note, you may be drilling a hole in the piano so that you have all this downward pressure when you need to be going up again, and the hole-drilling causes tension in the hand and arm, and maybe into your shoulders and torso.
So it's in this area of the ups and downs that we get into technique, which involves physics and the anatomy of the human body and the structure of the piano, combined with the sounds that you want to produce. Players of other instruments have to consider this from day 1 or they can't even produce a sound. The piano can be deceptive because for producing a note, even a cat pawing at the keys can "play the piano".