My mother was a terrific accompanist. She had a special gift. She could play by ear. That means she could remember the chord progressions to many songs and just make up the piano part on the spot.
When she was busy accompanying Handel's "Messiah" with a community choir in Ohio in about 1972, she slid down our icy walkway on the way to the performance. She broke three fingers on her left hand. She had my dad tape up those fingers, took an aspirin, then she got in the car saying, "The show must go on."
I asked her later, "How in the world did you do it?"
She shrugged and said, "Well, once I realized that Handel was a chords guy, I just played the fundamental bass notes with my thumb and first finger. It worked okay."
Playing by Ear is not something I was gifted to do. Perhaps it was because I didn't apply myself enough in Ear Training class in college or just didn't lie awake at night listening to the radio and analyzing chord progressions. Oh well, (sigh).
Anyway, I know that some of the ear training took. I decided that because I am a singer first, I listen melodically instead of harmonically. I can actually figure out chord progressions, albeit slowly, and not quickly enough to play by ear on the spot... unless it's just a 3-chord song like an old folk song.
But there is a silver lining to not relying upon being able to play by ear. I learned early on to notate music so that I could play it. Even before I studied at college, if I wanted to be able to play a song on the piano, I found that if I wrote it out, I could. And then, somebody else could come along and play it, too. Yeah, I may have to resort to the "hunt and peck" method of composition, but I can still get it done!