What is the main conflict in The Wild Muir: Twenty-two of John Muir's Greatest Adventures by John Muir?

Muir seems wholly unafraid of activities that would terrify any ordinary human being, such as charging grizzly bears to see how they run. In some stories, Muir comes almost to death but this is unclear from his own descriptions and those of others. After days of terrible and often life-threatening conditions, Muir still has enough strength to save experienced hikers who accompany him.