maybe it is the inverse. When you are successful in work and personal life you become confident. And they fuels more success/confidence. Basically you become more confident as and when you find more success.
Just adding to what dsr_ is saying, narcissists project confidence without actual success because their version of reality supports their correctness.
Narcissism/NPD is a result of the mind not being able to accept information that disproves their elevated sense of self worth. Anything that proves them wrong therefore is discarded before it can be processed internally. So when they speak with confidence, its because nothing in their reality can disprove what they are saying, even if what you're saying is true to our shared reality.
