Do what you know you can do well and don't overstretch yourself.

做你自己能做好的事情，不要超出自己的能力。

《柯林斯英汉双解大词典》

If you must move, don't follow a stream unless you know it, and in that case, you are not lost.

如果你非要走动的话，别顺着溪流走，除非你对它很熟悉。但是如果你很熟悉，那你就不会迷路了。

youdao

Keeping things short and sweet not only shows people that you are concise and don't waffle, but that you also know what you want.

亲切简洁的语言不仅彰显了你简明的个性，不会被误认为是在胡扯，还让对方知道你是一个知道自己想要什么的人。

youdao

When you're teenagers, you don't quite know what to write on there. Little Os and Xs for kisses and things like that.

VOA: special.2010.02.08

- You open Brooks and you find yourself really apart perhaps-- I don't know how well all of you are acquainted with the texts of Freud.

也许你们看布鲁克斯的作品时会觉得很头疼-,我不知道你们对弗洛伊德那几篇文章理解的如何了。

耶鲁公开课 - 文学理论导论课程节选

You are lost. You're in a new city and you're lost and you don't know where you're going.

你迷路了。你刚到一个城市，没法找到方向。你不知道你该怎么走。

How long课堂 - SpeakingMax英语口语达人

If somebody just drives up into your driveway and you're not home -- you don't know who these people are and you don't know how long it's going to take for the sheriffs to respond.

WHITEHOUSE: President Obama Speaks on Reducing Gun Violence

Finding satellites can be a major pain sometimes, and the signal can drop while you're driving (see video), which could be a major headache if you're on a trip and you really don't know where you're going.

ENGADGET: An Engadget adventure with TeleNav's G1 GPS software: hands-on, impressions, and video

You make dolls in a toy shop, and you shop for sofas, and, you, I don't know what you do.

NPR: 'Munich': Spielberg's Most Provocative Film Yet