What is the difference?
Why is this caring to a fault?
Because it holds the other responsible for my own sense of obligation, placing the burden of giving on someone outside myself. It is not carefree caring. It is anxious, heavy, laden with responsibility, like a job. It is the care of a first responder, or an unpaid volunteer.
Ultimately, this kind of caring, when offered to a child, friend or lover, will feel unfair to the caregiver. Resentment builds because they feel like they are owed something. Then they begin to exact payment from their loved ones. They get angry and withdraw, or both, and escape. They are like elastic bands that stretch beyond capacity then snap in your face.
The only person this is unfair to, is loved ones.
The caregiver-to-a-fault, in holding someone else responsible for their caring, refuses to see it comes from their own sense of duty. They want to feel good about themselves so they say "yes" when they should say "no", give without being asked, shower their gifts on you until they burn themselves out, then yell at you "NO!!!" when you ask for a glass of water...
That is caring to a fault and it is not sustainable.
True caring begins with me: feeling good about me, allowing me to be me, shedding my guilt and meeting my own needs first.
Me. Me. Me.
Then I can care freely about you.