How did luck or good fortune probably save Lewis and Clark's expedition?

The fact that Lewis and Clark were not savagely attacked
by animals was an example of luck.  Given the fact that the Louisiana Territory was
literally unknown, it was luck that the explorers did not wind up as victims of animal
attacks. The larger element of luck would have been their meeting up with Sacagawea.  It
was not planned nor was it thought of before the two embarked on their expedition that
they would find a Shoshone guide who was able to help them navigate and chart out the
territory.  Finding her and being able to rely on her for guidance and information
helped make the expedition a success and one that did not prove fatal.  It was another
in a long line of events where White settlers felt challenged and overwhelmed by the
magnitude of the nation, only to feel comforted and assured by the Native Americans. 
The sad truth of this would be that this comfort and reassurance gave way to control and
dominance down the dialectical path.