Why do the think tiny Tim death affects scrooge so deeply?

As a child Scrooge was abandoned in a bording school even at Christmas. He remembers the death of his own dear sister Fan and sees a glimmer of himself in Tiny Tim. When he is told by the Ghost of Christmas Presenty that he (the ghost) sees an empty chair by the fire and an unused crutch hanging on the wall Scrooge feels sorrow at the memories of loss he has experienced and ones which drove him to harden his heart.