Many aspects of our careers are things we cannot control but cause stress. A useless boss, endless deadlines, and too much work add to the issue. What also causes stress is the frustration that we cannot influence these things. But there are aspects to our careers we can influence.
Personal mastery is not something that you can only to help you deal with stress and improve you confidence. Actually, it is possible to apply mastery into you career as well. There are numerous studies showing personal mastery to have impact on your everyday life as well as with working effectively.