You can only give what you possess, and if you give all that you possess, then you will have nothing left for yourself. Giving to the point of self-detriment creates frustration, which leads to angst, which leads to anger. A person who feels empty will give grudgingly. Eventually, they will refuse to give at all. They may start to keep track of all that they do and use that information as ammunition against the person to whom they have given. They may start to demand things in return for even the smallest acts of kindness.