You do not understand.

They can choose to give that up anytime they want. A vocation is not something you can choose to walk away from any time you want.  A priest who leaves the priesthood is still a priest.  A parent is always a parent.  You cannot walk away from being a parent at any time, even if your child died.  You are still a parent.  

People can choose to define themselves by their careers if they want--but they can at any time walk away from it.  Vocations do not work like that.