Hétong yǐjīng qiān le, mùyǐ-chéngzhōu, zhǐnéng wǎng qián kàn.
The contract has been signed; what's done is done - we can only look forward.
Tips
memory
Imagine a tree that has been cut down and carved into a boat - once the wood (木) has become (成) a boat (舟), you can't turn it back into a tree. The action is irreversible.