The necessity or resolve to finish what one has started and reach one's goals despite any setbacks or difficulties encountered.

面对重重困难，我们要有开弓没有回头箭的决心，绝不轻言放弃。

Literally meaning a shot arrow cannot be retrieved, it refers to a situation where once an action has been initiated, it cannot be stopped or reversed.

既然决定了要投资，开弓没有回头箭，我们只能往前走了。