Which is an interpretation?

Composition about "the day i ran away" with 500 words

Which line from the story of my life by helen keller is an example of a simile? during the whole trip i did not have one fit of temper, there were so many things to keep my mind and fingers busy. i was like that ship before my education began, only i was without compass or sounding-line, and had no way of knowing how near the harbour was. one day, while i was playing with my new doll, miss sullivan put my big rag doll into my lap also, spelled "d-o-l-l" and tried to make me understand that "d-o-l-l" applied to both. child as i was, i at once felt the tenderness and sympathy which endeared dr. bell to so many hearts, as his wonderful achievements enlist their admiration.

London includes a quote about john thornton as he is observing hal attempt to motivate the exhausted dogs "it was idle, he knew, to get between a fool and his folly". if the word "idle" is defined as "of no real worth, importance, or significance", what does this statement mean with regard to hal? who is the fool? what is hal's folly? why would john thornton think it of no real worth or useless to intervene?