Keep the music you select on the correct side of this axis.
My students in Shades of Blue are working on the very difficult a cappella arrangement of “Almost Like Being In Love” by Darmon Meader. It’s aurally demanding, rhythmically tricky, and long!
It’s been hard work, but they haven’t complained much about the difficulty because it’s such a JOY to sing.
There are plenty of valid reasons to select a piece for an ensemble, but as you’re selecting music, it’s always wise to keep them above the difficulty-joy axis: that is, make sure the joy of the piece is at least as great as the difficulty.