Why might people see or remember things differently?

Because people experience the world differently.

Everything, from their point of view to the emotions they were feeling at the time, can influence how somebody remembers something.

in 1897, pershing became a tactical officer at west point, and that's where he was given the nickname "black jack." pershing's first name is "john," for which "jack" is a nickname, and he was a white man who commanded black troops. hence "black jack".