Yesterday in practice we had a lot of trouble. It's always very frustrating when rehearsal doesn't turn out as well as you'd like it to - when you're trying but just doing it wrong, when no one is blending properly, when the song just doesn't sound right.
On the other hand, I love the feeling when that frustration and that hard work and that exhaustion comes together, when suddenly the sound meshes and you sound beautiful. I love that feeling in music, and in essays, and in maths problems when you've been working for ages and then you just understand.
So the frustration is worth it.