Like others, it took me a while as an adult to know how to set boundaries. I am empathetic by nature but at the same time I'm a practical person, so if someone is suffering due to their own continued bad choices then my empathy drops to nil.
I have also wondered how those in the helping professions manage to do it year after year. I remember reading an article once about a priest on sabbatical whose only request was that no one ask him for anything. Made me realize how draining their daily life must be.