How did Anne Sullivan succeed in transforming Hellen Keller's life?

It's no exaggeration to say that, when Anne Sullivan came into Helen Keller's life, she transformed it completely. Prior to Anne's arrival, Helen was intensely frustrated by her disabilities, unable to establish any kind of meaningful connection with the world around her. Despite her family's best efforts, no one could reach her, and so she remained trapped in a world both literally and figuratively dark and silent.
At first, Anne herself found it hard to reach Helen too. But thanks to her enormous patience and determination, she persisted, until one day she finally made a remarkable breakthrough. While Anne and Helen were out walking through the fields one day, Anne was seized by a sudden flash of inspiration. She figured out a way to establish a connection between Helen and the natural world using sign language.
Anne placed Helen's hand under a water pump, and as the water gushed over it, Anne spelled out W-A-T-E-R over Helen's fingers. For the first time in her life, Helen was able to derive meaning from her surroundings. All of a sudden, the world was no longer such a hostile, scary place. Now it was a place of wonder, a place of learning, a place to be explored. Anne's flash of inspiration provided Helen with a key to unlock some of the secrets of the dark, silent world around her, setting her on a path of discovery that she would explore for the rest of her life.