Hard music gets easy with practice.
Often, the biggest challenge is to learn to speak the harmonic language the composer or arranger is using in the piece. Other times, it’s learning to express subtle meanings in the score. Learning to phrase effectively or sing physically demanding moments are regular challenges.
In all cases, hard music gets easy with practice.
The good news is that practice is additive: once you’ve surmounted the challenges of a certain piece, you’ll be able to apply that practice directly to similar pieces. It takes less time to learn to sing “Sing! Sing! Sing!” by the New York Voices, if you’ve already sung another NYV arrangement or two.
Practice can be on your own, and it must be with others in rehearsals and sectionals.
And it makes hard music easier.