Dear Rossming,
Thanks very much for your wonderful explanations! From your reply, I feel your level is higher.

As our mother tognue are Chinese, you may appreciate why I raise such question. Recently, I am going over all the new words I have touched this year! Since I wish to increase my interpretation level, every time I encounter a sentence which I can't get full idea of , I will make some effort to translate it. While translating, it is somewhat difficult to understand the sentence. The longman says one of the meanings of undercut is"make sth weaker or less effective" . It seems to me that the sentence can not be translated as "是不是缺乏信心使你信心减弱了". This translation ,obviously, doesn't suit Chinese habit. Therefore, I thought of the word "affect", because I think 影响 is better in the above Chinese sentence. By the way , could you give me your translation of the sentence!
With regards to your opinion that undercover is more vivid and picturisque. I quite agree with you. Recently I am feeling that Chinese is more logical while English is more picturisque. You will find it easier to understand a vocabulary if you can apply picturisque mind. Such word like distill,undercover, undercut,highlight,...
Waiting for your reply and instructions
Regards
Sky
