Niniane Wang (Google) said [via Google Blogoscoped]:
(…) problems usually occur due to mistakes rather than incompetence or indifference. (…) Not blaming means the cost of failure is tolerable. This allows people to feel free to innovate with high-risk high-reward ideas.
This is essential in combination with taking risks (see I’m so glad you made this mistake). It is not enough to encourage taking risks, it is also important to make sure that employees are protected from blame and sanctions if something doesn’t go according to plan. Sometimes you’re betting too high or on the wrong horse.