This is one of the lines that I remember:
The falcon cannot hear the falconer;
Things fall apart; the centre cannot hold;
Yeats, Easter: Too long a sacrifice
Mixed metaphors, but for some reason Yeats makes me think of To a Skylark by Shelley, specifically this line:
We look before and after,And pine for what is not:Our sincerest laughterWith some pain is fraught;Our sweetest songs are those that tell of saddest thought.