Mistakes are going to happen, no matter how hard we try to prevent them. Effective leaders do not allow the team to become paranoid about making mistakes. You cannot prevent them all. The principle is to try not to make the same mistake twice! Learn from mistakes. If people are not making mistakes, they are no trying new things. If they are making the same mistake twice, they are not learning new things!
A good team knows that it can take the risk to try, to fail, and to learn from its mistakes.