Because we don’t know how to learn from our mistakes. And to tell you the truth, most of us just don’t believe that we learn from our mistakes –they make the lot of the short-sighted ones. These people don’t realize the potential our mistakes have and hence, they are always vigilant. Taking every step with great precision, they forget that mistakes and failures are great teachers too. And this makes them afraid of committing mistakes.
As Rick Warren has said, “We are products of our past, but we don't have to be prisoners of it.” People who are afraid of committing mistakes, are actually afraid of becoming the prisoner of their past experiences. They don’t realize that the “product of past” is not just negative. It can be positive as well.
To put it in a better way, it’s only your approach and endeavor that decides that you have made mistake to progress further, or to get depressed with it and do even worse the next time, putting yourself into the vicious cycle of continuous mistakes. The only escapade in such cases, is your positive approach and attitude towards life, its failures, and the mistakes you commit in it.