Helen Keller, in her autobiography, The Story of My Life, recounts the most important and significant events that shape her future and contribute to her learning "from life itself." Helen begins her autobiography with a sense of trepidation, aware that she must expose herself and remind herself of some of the painful experiences as well as the inspiring and motivational aspects of her first 22 years.
As with any autobiography, the experiences and events are Helen's own interpretation and she is acutely aware of difficulties with potentially telling someone else's story - as she reveals later in The Story of My Life when she accidentally wrote her own story but took it from another published work. She constantly worries whether her thoughts are actually original.
Helen admits that there are certain instances that she remembers most prominently but there are others that lurk in her memory but that she cannot recall accurately or even at all. These are the "shadows of the prison-house." (Ch 1). As much of Helen's early life was a "silent dayless life," she is referring to her own thoughts and mind as the "prison-house." The events that she cannot recall or that are confusing can be found in the "shadows."