打退堂鼓 [- - tánɡ ɡǔ](比喻遇到困难就撒手不干) beat a retreat; back out; draw [pull; haul] in one's horns; withdraw from ...; give up a pursuit without attaining the [one's] goal; give up：
•¶ 不要遇到一点困难就打退堂鼓。 Don't back up the moment you run up against a little difficulty.