Helen Keller, known as a pioneer in the education and advocacy of the deafblind, has an episode so famous that it's hard to resist returning to it.
Keller lost her sight and hearing to an illness at one year and seven months old, and because she had acquired no language before that, the frustration of being unable to communicate her wishes drove her into fierce tantrums, day after day.
One day, not long before she turned seven, Anne Mansfield Sullivan arrived at Keller's home as her tutor. From the moment she took up the post, Sullivan devotedly spelled out words like "mug" and "water" into Keller's palm using finger spelling. But Keller simply found it amusing as nothing more than finger movements, without understanding that these were words carrying meaning.
The turning point came roughly a month later. The two were out on a walk and went to the well house, where someone was pumping up water, and Keller held out her hand toward it. As cold water poured over one hand, Sullivan spelled "w-a-t-e-r" into the palm of her other hand.