表达“play it by ear”源于音乐，就是说不用看乐谱凭耳朵和记忆就能弹奏出乐曲。现在这个说法的意思可以引申为“根据事情的发展情况来决定下一步怎么做”，也就是“见机行事、边走边看”。 

例句

I can't promise I can make it tonight. Let's play it by ear.

我不能确保我今晚能来。到时候看情况再定。

We should play it by ear. Don't make any decisions just yet.

我们应该见机行事。别现在就做决定。

I am not sure what the tour guide has in plan for us today, so I'll just play it by ear.

我还不清楚导游今天给我们做了什么安排，所以打算到时候看情况再做决定。