A good state of mind is the foundation (this is probably a better word) of success 

Life is a sophisticated (I don't think this is the word you want - what are you trying to describe?) journey where we encounter the upsetness (not a word :) ) and dissatisfaction, and it is difficult to avoid. which we can’t escape from. Just bear in mind that a good state of mind is the foundation of success.

An incident rushes back as the tide (maybe better to say, "I remember a time when I was upset.") With a final exam drawing near, I concentrated more on my studies because I feared of the failure. Consequently, I was not myself in class.Seeing this and concerned my fitness about me, my mum just made every endeavours (this is not incorrect, but maybe better to say "helped me") to relax my mind and outdoor life (do you mean you went outside to relax?).  In the company of my mum,I gradually adjusted myself to the exam and greeted the exam with in a more constructive state of mind. In the end,I passed the exam without burdens.

A light heart can go further.It’s out of the question that we have the competence that anticipating the obstacles of our lives. (better phrase:  "It's not possible to anticipate every obstacle of our lives").  Only by equipping ourselves with a good state can we keep calm and go over them without hesitation.

Yinny, I know I wrote many corrections here, but they are primarily grammatical and "flow."  I knew what you were trying to say and understood your story!  Keep practicing your writing, this was very good, and it's also very true!  Well done. :-)