midstream 中流; 中游，don’t change horse midstream不要在中途换马，也就是不要中途变卦，转换策略的意思。

【例句】
Now that you have made your choice, don't change horse midstream.
既然你已经做好了选择，就不要中途变卦。

Our president may have made a few mistakes, but don’t change horses in the middle of the stream.
我们的校长可能犯了些错误，可在如此险恶的形势下，换人却不是时候。