Expressing “Once... Then...” with “yídàn... jiù...”

一旦决定了目标，就应该坚持到底。

Yídàn juédìng le mùbiāo, jiù yīnggāi jiānchí dàodǐ.

Once you have decided on a goal, you should persist to the end.

这种问题一旦处理不好，就可能带来更大的麻烦。

Zhè zhǒng wèntí yídàn chǔlǐ bù hǎo, jiù kěnéng dài lái gèng dà de máfan.

Once this kind of problem is not handled properly, it may bring even greater trouble.

合同一旦签了，很多事情就不能轻易改变。

Hétong yídàn qiān le, hěn duō shìqing jiù bù néng qīngyì gǎibiàn.

Once the contract is signed, many things cannot be changed easily.