If you don't make your choice in time, you are likely to fall between two stools.

如果你不及时作出决定，就会两头落空。

《新英汉大辞典》

You'd fall between two stools.

你会两头落空的。

youdao

Between two stools one falls to the ground.

两者之间的粪便一次落到地面。

youdao

Britain is in danger of falling between two stools: on the one hand, rejecting state finance and on the other, discouraging individual donation.

ECONOMIST: Campaign financing

Hussey, who was threatening to come out of his shell, was now caught between two stools - and his decision to leave a Harbhajan top-spinner was fatal.

BBC: Australian pair dent Indian hopes