It is easy to switch careers?

[Bookwormlux]

There are situations where people tend to develop passion for something else outside what they may have studied in school and this makes them to not use their certificate again after graduation. They tend to shift focus to fields like programming, software development, and related fields which would be more rewarding both financially and other wise. Some times, it may even involve people resigning from their jobs and going for a different career that they have got passion for.
Do you think it is easy to cope in a new career after you must have mastered your former one? Like a doctor resigning to venture into music and entertainment.
What do you think?