You have good ideas..
Here are a few suggestions to improve your essay.
Success means different things to different people.
.... This is good point. Try presenting it in a better manner.
Different people have different opinions on what success is.For some, success is about being successful in your career which is by working in a good company or getting a really good salary, others thinks that success is about being good at school or university and getting good marks. Yet others think that success is about being successful in life.
You have said "others think" twice in a short gap. It sorts of breaks the nice flow of your essay up to that point.
Many believe success is about having a great job with a really good salary. Others believe it is about getting good grades at school and university. Only a very few people think that it is about having pleasant and prosperous life.Cause less in confidence from my opinion leads to inaction and shyness.
In my point of view, being less confident makes one shy and inactive.In fact, I had a friend in my school and he has a really strong voice actually, an amazing voice but he had a lack in confidence and of course that made him shy but then he had the chance to sing in front of a huge crowed, it was a contest between the schools and he can won that easily but he didn't even participate because he is shy and he was afraid of what people would do and think about him so he missed an opportunity to be successful because he don't have confidence in himself.
This sentence is too long. And it sounds as if you are talking to yourself. Try to break it down.
I had a shy friend who had a very strong voice. One day he got the opportunity to sing in front of a large crowd and win our school a contest. He could ahve won it easily with the amazing voice he had. But due to his lack of confidence he did not even take part in the competition.