1.The first enemy that you’ve got to destroy before it destroys you is indifference.

【参考译文】第一个你要在它袭击你之前将其击败的敌人是冷漠。
【结构解析】句子的主干是"The first enemy...is indifference"，“that you’ve got to destroy before it destroys you”做定语从句，修饰“the first enemy”，句中的"it"指“the first enemy”。

2.But you can’t let worry loose like a mad dog that drives you into a small corner.

【参考译文】但你不能让担忧像疯狗一样失控，将你逼至死角。
【结构解析】句中使用了let sb. do sth.的结构，“loose”的行使者是"worry"，"that drives you into a small corner"做定语从句，修饰“mad dog”。

3.Be courageous in your life and in your pursuit of the things you want and the person you want to become.

【参考译文】要勇敢地生活，勇敢地追求你想要的事物并勇敢地成为你想成为的人。
【结构解析】“in your life ”和“ in your pursuit of ...”同时做“be courageous”的状语。