What do i check in a book to make sure it is a valuable source?

Which link would readers of this dictionary entry click if they wanted more information about the historical origins of the word language

Why college athletes should not get paid to play conclusion

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?