I was seated at the piano, playing for the first time the last piece in Moussorgsky's Pictures At An Exhibition. It's a majestic and stately piece for one player, called "The Great Gate of Kiev," with some awkward parallel octaves in the left hand, but most of it is a series of chords, not too difficult until near the end.
It gets difficult in the 13th measure before the end, because Moussorgsky (who died on this date in 1881) calls for the player to play three grace notes, followed by 11 simultaneous whole notes, five with the right hand and six with the left hand. Moussorgsky expects both of the player's hands to span two octaves each. That's four to five more white keys than the typical hand can span.
He calls for three grace notes and another 11 simultaneous whole notes in the next measure, and again three measures after that.
Most of Moussorgsky's customers don't have 11 fingers. Nor can they span two octaves with each hand. This isn't the only reason that Moussorgsky doesn't have the market share of Tchaikovsky or Prokofiev, but it sure doesn't help.