run out of steam

这个短语的典故显然是来自蒸汽机，当驱动锅炉的能量太少而不能产生蒸汽时，蒸汽机逐渐减速，然后停止。就像人们泄气的过程。

to suddenly lose the energy or interest to continue doing what you are doing

忽然失去动力;顿时泄气;突然没了兴趣

The peace talks seem to have run out of steam.

和谈好像突然失去了动力。