paint the Forth Bridge 永无止尽的任务

原指苏格兰中部的福斯铁路大桥表面刷漆的浩大工程，据说等到把桥梁全部油漆一遍之后，前面的已经褪色，就又得开始重新油漆了，所以paint the Forth Bridge意为永无止境的或艰巨的任务。

例：

Keeping the county's roads in good shape is like painting the Forth Bridge because as soon as you've resurfaced a stretch of road, it begins to deteriorate again due to the number of vehicles which travel along it.

维持国内公路的良好状态简直是做不完的工作，因为你刚刚把一段路面重新铺好，它就又开始因为每天在路上跑的大量车辆而磨损了。