Sentence:  Among the greatest physician-scientists of our time, Mike Brown and Joe Goldstein argue that the trainee is ready to <WSD>leave the nest</WSD> when she or he has acquired technical courage, a sufficient set of skills and experience and self-confidence to develop new tools when the need arises. 
Meaning of the word marked with <WSD> tags:  To become independent; To begin to act without supervision or in ways that are not prescribed.